regex to find text plus trailing 10+ spaces sum of two matches’ lengths is part of matching condition
Regex to Find Text Plus Trailing 10+ Spaces; Sum of Two Matches’ Lengths is Part of Matching Condition
At revWhiteShadow, we understand the nuances of working with terminal output, especially when it’s captured through copy-pasting. A common, albeit frustrating, issue arises when terminal sessions are logged, and lines that should be distinct become unnaturally elongated due to trailing spaces. This phenomenon, often invisible within the terminal itself but glaringly apparent in text editors and Integrated Development Environments (IDEs), can corrupt data processing and analysis workflows. This article provides a comprehensive guide, utilizing advanced regular expressions and scripting techniques, to precisely identify and rectify these problematic lines, ensuring data integrity and cleaner log files. We aim to offer solutions that are not only effective but also efficient, catering to various tools and preferences, from Raku and Perl to Sed and Awk, and even enhancing Bash scripting capabilities.
Understanding the Core Problem: Trailing Spaces and Terminal Width
The crux of the issue lies in how terminal emulators, particularly Cygwin’s mintty, handle output when it reaches the defined terminal width. When commands or their outputs extend to the very edge of the terminal display, instead of simply breaking to the next line, some terminals might pad the remainder of the line with spaces to reach a predefined width. This padding is often transparent within the terminal itself, as the visual rendering might not clearly distinguish between a natural end-of-line and one padded with spaces. However, when this content is copied and pasted into a text file for later processing, these trailing spaces become significant.
The problem intensifies when the sum of the characters in a command and the subsequent trailing spaces, up to the point where a new, non-space character appears, equals the terminal’s column width (e.g., 80 characters). This specific condition is what makes detection and correction challenging, as a simple line break might appear, but the underlying structure is a single, over-padded line. Our goal is to devise a method that can identify these specific patterns: a line of text (the command), followed by ten or more spaces, and then a non-space character (the output or continuation). Crucially, the sum of the length of the initial text and the length of the trailing spaces must be equal to the terminal width, and this calculation must accurately account for UTF-8 encoded characters.
The Significance of UTF-8 Character Encoding
In modern computing, robust text handling necessitates adherence to standards like UTF-8, which supports a vast array of characters from different languages and symbols. When dealing with terminal output that may contain international characters (such as the example “Cédric,Žemaičių Naumiesčio” or “你好。我不知道。”), byte-level counting for character length is insufficient. UTF-8 characters can span multiple bytes, meaning a simple wc -c or similar byte-counting mechanisms will yield incorrect results. Our solutions must inherently understand and correctly count UTF-8 characters. This is a critical requirement for accurate length calculations and for meeting the condition where the combined length of the text and spaces equals the terminal width.
Advanced Regex Solutions for Identifying Problematic Lines
To tackle this, we need regular expressions capable of capturing the pattern: text, followed by at least ten spaces, and then more text, all while ensuring the combined length of the initial text and the spaces meets the terminal width criterion.
Raku and Perl: Powerful Pattern Matching for UTF-8
Raku (formerly Perl 6) and Perl offer sophisticated regular expression engines that are well-equipped to handle UTF-8 correctly. Their capabilities extend to advanced lookarounds and conditional matching, making them ideal for this task.
Raku Solution: Precise UTF-8 Character Counting and Conditional Matching
Raku’s strengths lie in its native understanding of Unicode and its powerful regex syntax. We can construct a regex that captures the desired pattern and incorporates the length constraint.
Consider the following Raku approach. The core idea is to match:
- The initial text:
(.*?)- This non-greedily captures any character. - Ten or more spaces:
[ ]{10,}- This matches a literal space character repeated ten or more times. - The trailing text:
(.*)- This greedily captures the rest of the line.
The challenge is incorporating the length condition. Raku allows embedding code within regexes, enabling us to perform these checks dynamically.
# Assume $terminal_width is set to your terminal's width, e.g., 80.
my $terminal_width = 80;
# Read the log file line by line
my @lines = '... your log file content ...'.split("\n");
for @lines -> $line {
# Regex to capture the components: initial text, 10+ spaces, and subsequent text.
# The `(:|)` construct allows us to check conditions based on captured groups.
if $line ~~ m/(.*?)([ ]{10,})(.*)/ {
my ($initial_text, $spaces, $trailing_text) = $0, $1, $2;
# Calculate lengths using Raku's char count capability
my $len_initial = $initial_text.chars;
my $len_spaces = $spaces.chars;
# Check if the sum of initial text length and space length equals terminal width
if ($len_initial + $len_spaces) == $terminal_width {
# We've found a problematic line.
# The original line is: $line
# We want to replace it with: $initial_text + "\n" + $trailing_text
print "Original: $line\n";
print "Corrected: $initial_text\n";
print "$trailing_text\n";
print "--------------------------\n";
}
}
}
Explanation of the Raku Regex:
m/(.*?)([ ]{10,})(.*)/: This is the primary matching operation.(.*?): This is the first capturing group. It non-greedily matches any character (.) zero or more times (*). The?makes it non-greedy, meaning it will match the shortest possible string. This captures the initial command or text.([ ]{10,}): This is the second capturing group. It specifically matches a literal space character ({10,}). This identifies the problematic padding.(.*): This is the third capturing group. It greedily matches any remaining characters on the line. This captures the output or the text that follows the excessive spaces.
Refining the Raku Solution with Conditional Logic:
Raku’s ability to embed code within the regex is powerful. We can directly check the length condition within the matching process for greater efficiency.
# Assume $terminal_width is set to your terminal's width, e.g., 80.
my $terminal_width = 80;
# Process the log file line by line
# For demonstration, we'll use a sample string. Replace with file reading.
my $log_content = q~
$ tput cols 80
$ type wc # OK
wc is hashed (/usr/bin/wc)
$ # This one is fine. OK
$ echo "Cédric,Žemaičių Naumiesčio" Cédric, Žemaičių Naumiesčio
$
~;
for $line ( $log_content.split("\n") ) {
# The core regex with embedded conditional length check
# (.*?): captures the initial text
# ([ ]{10,}): captures 10 or more spaces
# (.*): captures the rest of the line
# The inner `||` is a short-circuiting OR. If the first part fails, it tries the second.
# The `<?{...}>` is a post-condition asserting that the code block returns true.
if $line ~~ m/(.*?)([ ]{10,})(.*) <?{ $^MATCH[1].chars + $^MATCH[2].chars == $terminal_width }> / {
my ($initial_text, $spaces, $trailing_text) = $^MATCH[1], $^MATCH[2], $^MATCH[3];
# Print the corrected output
print "Found problematic line:\n";
print "$line\n";
print "--- Corrected to ---\n";
print "$initial_text\n";
print "$trailing_text\n";
print "--------------------\n";
}
}
Key Raku Features Used:
m/.../: The match operator..*?: Non-greedy match for initial text.[ ]{10,}: Matches 10 or more literal spaces..*: Greedy match for trailing text.$^MATCH: Special variable in Raku that refers to the match object.$^MATCH[1]refers to the content of the first capturing group.chars: Method to count Unicode characters correctly.<?{...}>: A conditional assertion. The code within the braces is executed, and if it evaluates to true, the match continues. This is where we place our length check.
Perl Solution: Leveraging lookbehind and length
Perl’s regular expressions are also very powerful, with features like lookarounds and the ability to call functions within regexes.
#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use feature 'say'; # For modern Perl say function
my $terminal_width = 80; # Set your terminal width here
# Sample log content (replace with reading from a file)
my $log_content = <<'END_LOG';
$ tput cols 80
$ type wc # OK
wc is hashed (/usr/bin/wc)
$ # This one is fine. OK
$ echo "Cédric,Žemaičių Naumiesčio" Cédric, Žemaičių Naumiesčio
$
END_LOG
# To enable UTF-8 for input/output, ensure your locale is set correctly or use:
# binmode(STDIN, ":encoding(utf8)");
# binmode(STDOUT, ":encoding(utf8)");
my @lines = split "\n", $log_content;
foreach my $line (@lines) {
# Regex breakdown:
# (.*?) : Capture group 1: Initial text (non-greedy)
# ([ ]{10,}) : Capture group 2: 10 or more spaces
# (.*) : Capture group 3: Trailing text (greedy)
#
# The `(?{ ... })` is an embedded code block that executes.
# It captures the lengths and checks the condition.
# This approach requires careful construction to ensure correct grouping and length calculation.
# A more direct approach uses `length` on captured groups after a preliminary match.
if ($line =~ /^(.*?)(\s{10,})(.*)$/) { # Initial match for structure
my $initial_text = $1;
my $spaces = $2;
my $trailing_text= $3;
# Use Perl's `length` function, which correctly counts characters in UTF-8 strings
# when the appropriate modules/pragmas are used.
# The `use utf8;` pragma and `use feature 'unicode_strings';` (or `use v5.10;` or later)
# are crucial for correct character counting.
if (length($initial_text) + length($spaces) == $terminal_width) {
say "Found problematic line:";
say "$line";
say "--- Corrected to ---";
say "$initial_text";
say "$trailing_text";
say "--------------------";
}
}
}
Key Perl Features Used:
use strict; use warnings;: Essential for writing robust Perl code.use utf8;: Enables UTF-8 handling for source code and potentially for I/O.length(): Perl’s built-in function to get the length of a string. Whenuse utf8and appropriate locale settings are in place, this correctly counts UTF-8 characters.($initial_text, $spaces, $trailing_text) = ($1, $2, $3): Assigning captured groups from the regex match.(\s{10,}): A more concise way to match 10 or more whitespace characters. However, for exact space padding,([ ]{10,})is more precise if other whitespace characters are not intended. Given the problem description,([ ]{10,})is preferred.
Sed and Awk: Stream Editing for In-Place Transformations
Sed and Awk are powerful stream editors ideal for processing text files line by line and performing search-and-replace operations. They are commonly used within Unix-like environments, including within Vim.
Sed Solution: Conditional Replacement
Sed’s strength lies in its pattern-action model. We can use its regex capabilities to find the problematic lines and then substitute them. The main challenge with Sed is performing the length calculation directly within the s command. This often requires creative use of the t command or multiple passes, or a more advanced approach using the hold space.
A more practical Sed approach might involve a preliminary step to identify lines and then a replacement. However, for the specific condition of length(text) + length(spaces) == terminal_width, Sed alone can become complex. Let’s consider a Sed script that assumes a fixed width and uses a slightly less dynamic approach for illustration.
#!/bin/bash
TERMINAL_WIDTH=80 # Define the terminal width
# Assuming your log file is named 'terminal_logfile_woes.log'
# Create a temporary file to store replacements
TMP_FILE=$(mktemp)
# Use awk to perform the detailed check and output lines to be modified
# Then use sed to perform the actual replacement on those identified lines.
# This is often more manageable than a single complex sed command.
# First, identify lines that match the structure: text, 10+ spaces, non-space char
# And then filter those where text length + space length = TERMINAL_WIDTH.
awk -v width="$TERMINAL_WIDTH" '
{
# Use match() to find the pattern: start, 10+ spaces, end.
# match(string, regex, array_to_hold_matches)
# The regex captures three parts: initial text, spaces, trailing text.
if (match($0, /^(.*)([ ]{10,})(.*)$/, m)) {
initial_len = m[1] ? length(m[1]) : 0; # Length of initial text
space_len = m[2] ? length(m[2]) : 0; # Length of spaces
# Check if the sum of initial text and spaces equals the terminal width
if ((initial_len + space_len) == width) {
# Output the modified line: initial text followed by a newline and the trailing text
print m[1] "\n" m[3];
} else {
# If the condition is not met, print the original line.
print $0;
}
} else {
# If the pattern itself doesn't match, print the original line.
print $0;
}
}' terminal_logfile_woes.log > temp_processed_log.txt
# Now, you can either replace the original file with the processed one
# mv temp_processed_log.txt terminal_logfile_woes.log
# Or view the difference and decide on further action.
echo "Processed log saved to temp_processed_log.txt"
Explanation of the Awk Solution:
awk -v width="$TERMINAL_WIDTH" '...' terminal_logfile_woes.log: This invokesawkwith theTERMINAL_WIDTHvariable passed in.match($0, /^(.*)([ ]{10,})(.*)$/, m): This is the core of the identification.$0: Represents the entire current line./^(.*)([ ]{10,})(.*)$/: The regex.^: Matches the beginning of the line.(.*): Captures the initial text (Group 1).([ ]{10,}): Captures 10 or more spaces (Group 2).(.*): Captures the trailing text (Group 3).$: Matches the end of the line.
m: An array whereawkstores the captured substrings.m[1]will be the initial text,m[2]the spaces, andm[3]the trailing text.
initial_len = m[1] ? length(m[1]) : 0;: Calculates the length of the initial text, handling cases wherem[1]might be empty.length()inawkcorrectly handles multi-byte characters if the locale is set appropriately (e.g.,LC_ALL=en_US.UTF-8).space_len = m[2] ? length(m[2]) : 0;: Calculates the length of the spaces.if ((initial_len + space_len) == width): This is the critical condition check.print m[1] "\n" m[3];: If the condition is met, the line is reformed with a newline character separating the initial text and the trailing text.print $0;: If the condition is not met or the pattern doesn’t match, the original line is printed as is.
This awk approach is robust and handles the UTF-8 character counting correctly provided the awk implementation and environment locale are configured for UTF-8.
Sed for Replacement (if you can identify lines first)
If you have a way to identify the problematic lines (e.g., using grep or awk as shown above), sed can be used to perform the substitution. For instance, if awk outputs the lines that need changing to a temporary file, you could then use sed to replace them in the original file. However, the awk solution above is more direct for processing the entire file in one go.
A more advanced sed approach might involve reading the line, capturing its length, and then using t commands, but this quickly becomes convoluted for conditional length checks. The awk solution is generally preferred for its clarity and directness in handling such logical conditions.
Bash Scripting: Enhancing Your Clunky Solution
The provided Bash script is a solid attempt and demonstrates a good understanding of Bash’s string manipulation and regex capabilities. Let’s refine and enhance it, focusing on clarity and potentially improving the UTF-8 handling aspect.
The core of the Bash solution is the regex matching and subsequent length checks using ${#variable}.
#!/bin/bash
# Function to find and fix terminal log lines with excessive trailing spaces.
# Handles UTF-8 characters correctly for length calculations.
find_spaces_not_linefeed() {
local input_logfile_name="$1"
local terminal_width="${2:-80}" # Default terminal width to 80
local do_check="${3:-0}" # Default do_check to 0 (no verbose checking)
if [ -z "$input_logfile_name" ]; then
echo "Usage: find_spaces_not_linefeed LOGFILE [TERMINAL_WIDTH] [DO_CHECK]"
return 1
fi
if [ ! -f "$input_logfile_name" ]; then
echo "Error: File '$input_logfile_name' not found."
return 1
fi
local change_count=0
local current_line=""
# Use process substitution to read lines, allowing for more robust handling.
# LC_ALL=en_US.UTF-8 ensures that character counting functions work with UTF-8.
# This needs to be set in the environment where the script is run.
while IFS= read -r current_line || [[ -n "$current_line" ]]; do
# Regex:
# ^(.*?) : Capture group 1: Initial text (non-greedy)
# ([ ]{10,}) : Capture group 2: 10 or more literal spaces
# ([^ ]*)$ : Capture group 3: Trailing characters that are NOT spaces, until the end.
# This ensures we capture the output after the padding.
if [[ "$current_line" =~ ^(.*?)([ ]{10,})([^ ].*)$ ]]; then
local beg="${BASH_REMATCH[1]}"
local spaces="${BASH_REMATCH[2]}"
local end="${BASH_REMATCH[3]}"
# UTF-8 aware length calculation for bash:
# We can use `printf %s "$string" | wc -m` or `printf %s "$string" | wc -m`
# or, more directly within bash for character count if available,
# but the standard way is `printf %s | wc -m`.
# Let's ensure the environment is set for UTF-8.
# The ${#var} syntax counts bytes, not UTF-8 characters.
# We need a separate tool for character counting.
# `wc -m` is the most portable way.
local len_beg=$(printf "%s" "$beg" | wc -m)
local len_spaces=$(printf "%s" "$spaces" | wc -m)
local len_end=$(printf "%s" "$end" | wc -m) # Not strictly needed for the condition, but good for debugging
if [ "$do_check" -ne 0 ]; then
echo ""
echo "# FOR CHECKING #"
echo -n "len_beg: ${len_beg} "
echo -n "len_spaces: ${len_spaces} "
echo "len_end: ${len_end}"
fi
# The core condition: sum of initial text length and space length equals terminal width.
# Note: The calculation is $( ( ... ) )
if [ $(( len_beg + len_spaces )) -eq "$terminal_width" ]; then
change_count=$((change_count + 1))
if [ "$do_check" -eq 0 ]; then echo ""; fi
echo " CHANGE"
echo "${current_line}"
echo " TO"
echo "${beg}" # Output initial text
echo "${end}" # Output trailing text on a new line
echo "##### WITH a linefeed and not spaces."
fi
fi
done < "$input_logfile_name" # Process the input file
if [ "$change_count" -eq 0 ]; then
echo "No matches found. No changes needed."
else
echo "Total changes made: $change_count"
fi
}
# --- Example Usage ---
# To use this function, first define it in your shell or source it from a file.
# Then call it like:
# find_spaces_not_linefeed your_log_file.log 80
# For demonstration purposes, let's simulate the file content and call the function.
# In a real scenario, you would have the file.
# Create a dummy log file for testing
cat << EOF > test_log_file.log
$ tput cols 80
$ type wc # OK
wc is hashed (/usr/bin/wc)
$ # This one is fine. OK
$ echo "Cédric,Žemaičių Naumiesčio" Cédric, Žemaičių Naumiesčio
$
EOF
echo "--- Running find_spaces_not_linefeed on test_log_file.log ---"
# Ensure your terminal supports UTF-8 and the locale is set.
# For example, in your shell before running: export LC_ALL=en_US.UTF-8
# Or if you are in a different locale, ensure it handles UTF-8.
# The 'wc -m' command relies on the locale.
# You can also add the DO_CHECK flag to see lengths:
# find_spaces_not_linefeed test_log_file.log 80 1
find_spaces_not_linefeed test_log_file.log 80
# Clean up the dummy file
# rm test_log_file.log
Enhancements to the Bash Script:
- UTF-8 Character Counting: The most significant improvement is using
printf "%s" "$variable" | wc -mfor length calculation. The${#variable}parameter expansion in Bash counts bytes, not characters.wc -mcounts characters correctly, provided theLC_ALLenvironment variable is set to a UTF-8 locale (e.g.,en_US.UTF-8). This is crucial for accurate results with international characters. - Robust
read:while IFS= read -r current_line || [[ -n "$current_line" ]]is a more robust way to read lines, ensuring that the last line of a file is processed even if it doesn’t end with a newline character. - Clearer Variable Names: Using
beg,spaces, andendwithin the script is good practice. - Default Arguments: The function now accepts
TERMINAL_WIDTHandDO_CHECKwith default values, making it more flexible. - Error Handling: Added checks for file existence and argument presence.
- Regex Refinement: The regex
([^ ].*)$for the trailing part ensures we capture non-space characters following the padding.
This refined Bash script leverages external tools (wc -m) to overcome Bash’s byte-counting limitation, making it a powerful solution for your specific problem, especially when dealing with UTF-8 encoded logs.
Practical Application: In-Place Editing and Workflow Integration
Modifying Files In-Place
For any of these solutions, the ability to modify files in-place is highly desirable for streamlining your workflow.
Perl/Raku: These languages can easily read a file, process its content, and write the modified content back to the same file (or a new one). You’d typically read the entire file content into a string, perform replacements, and then overwrite the original file.
# Example Perl for in-place editing (use with caution!) my $filename = "your_logfile.log"; my $terminal_width = 80; # Read the entire file content open my $fh, '<:encoding(utf8)', $filename or die "Cannot open $filename: $!"; my $content = do { local $/; <$fh> }; close $fh; # Process content (using a similar logic as above) my $new_content = ""; foreach my $line (split "\n", $content) { if ($line =~ /^(.*?)(\s{10,})(.*)$/ && (length($1) + length($2) == $terminal_width)) { $new_content .= "$1\n$3\n"; # Replace with newline } else { $new_content .= "$line\n"; # Keep original line } } # Overwrite the original file open my $fh_out, '>:encoding(utf8)', $filename or die "Cannot open $filename for writing: $!"; print $fh_out $new_content; close $fh_out;Awk: Awk can write to a temporary file and then atomically replace the original file.
# After running the awk command: mv temp_processed_log.txt terminal_logfile_woes.logBash: The Bash script, as presented, prints the modified output. To achieve in-place editing, you would redirect its output to a temporary file and then move it over the original.
# Assuming your function is defined or sourced find_spaces_not_linefeed terminal_logfile_woes.log 80 > temp_output.log mv temp_output.log terminal_logfile_woes.log
Integration with Vim
For users who prefer to work within Vim, sed and awk are excellent choices because they can be executed directly from within the editor.
Using
sedin Vim: You can use Vim’s:scommand combined with:globalor:argdoto apply replacements. For complex logic involving length checks thatsedalone struggles with, you might use Vim’s scripting capabilities or call external scripts. A common pattern is to use:r !commandto read the output of a command into the buffer, or:w !commandto pipe the buffer content to a command.If you had a
sedcommand that could do the replacement directly, you’d use::1,$!s/regex/replacement/g(with appropriate regex and replacement).Using
awkin Vim: You can executeawkcommands from Vim::%!awk -v width="80" '...'This command pipes the entire current buffer toawkand replaces the buffer withawk’s output.
Handling Edge Cases and Robustness
While our solutions are designed to be precise, consider these edge cases:
- Varying Terminal Widths: The scripts accept
TERMINAL_WIDTHas a parameter, which is crucial. If you don’t know the original terminal width, the script might not perform correctly. For logs where width varied, you might need more sophisticated logic or multiple passes. - Inconsistent Padding: The requirement is for 10 or more spaces. If there are fewer than 10 spaces, or if there are no spaces at all, the current regex won’t match. This is by design, as we are targeting the specific problem of excessive padding.
- UTF-8 Locale: Ensure your environment is set up correctly for UTF-8 processing. For Bash scripts,
export LC_ALL=en_US.UTF-8before running is recommended. For Perl/Awk, theuse utf8pragma and locale settings are key. - Non-Monospaced Fonts: As noted in the original question, true monospacing across all Unicode characters is rare. While our solutions correctly count UTF-8 characters, the visual alignment in different fonts can still be a factor. However, for the purpose of fixing the captured log data, character count is the correct metric.
Conclusion: Achieving Cleaner Terminal Logs
By leveraging the power of Raku, Perl, Awk, and sophisticated Bash scripting, we can effectively identify and rectify terminal log lines suffering from excessive trailing spaces that span the terminal width. The key is to use regular expressions that accurately capture the pattern of text followed by ten or more spaces, and importantly, to implement character-aware length calculations that respect UTF-8 encoding.
At revWhiteShadow, we advocate for precise and efficient data cleaning. The solutions provided here offer robust mechanisms to ensure your log files are accurate, free from the distortions of copy-pasting, and ready for any subsequent analysis or processing. Whether you prefer the elegance of Raku, the versatility of Perl, the stream-editing prowess of Awk, or the enhanced control of Bash, you now have the tools to tackle this common terminal logging challenge head-on, ensuring your data integrity remains paramount.