grep & awk regex to print next word after pattern match

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The world of computing is deeply intertwined with the realm of text processing. Every configuration file you've edited, every script you've executed, every data you've analyzed – they all revolve around the manipulation of text. This manipulation becomes a pivotal skill when operating in Unix-like environments, where even the most complex operations can often boil down to filtering and transforming text data.

 

Grep: More Than Just Matching

grep is an indispensable tool in the Unix toolkit. Its name derives from the command sequence in the original Unix text editor ed: g/re/p (globally search for a regular expression and print). Over the years, grep has evolved from a simple pattern searcher to a versatile text processing utility.

For grep, especially when using the -P (Perl-compatible) option, the fundamental idea is to use the \K escape sequence, which allows the tool to "reset" the start of the reported match.

grep -oP 'PATTERN\KTARGET'

 

Syntax to capture content after a Pattern using grep

Here is a table covering some use cases of grep and match:

Usage Scenario Command Syntax Description
Word After Match grep -oP 'PATTERN\K \S+' Matches the word immediately after the given PATTERN. \S+ captures non-whitespace characters.
Multiple Words After Match grep -oP 'PATTERN\K \S+ \S+' Matches the next two words after the PATTERN. Adjust \S+ repetitions for more words.
Everything After Match grep -oP 'PATTERN\K.*' Matches and returns everything after the PATTERN until the end of the line.
Specific Characters After Match grep -oP 'PATTERN\K.{N}' Captures a specific number of characters (N) after the PATTERN. Replace N with a number.
Non-greedy Matching grep -oP 'PATTERN\K.*?ENDINGPATTERN' Uses non-greedy matching to capture content until it encounters an ENDINGPATTERN.

Key Points to Remember:

  • -o: Outputs only the matched portion of the input.
  • -P: Enables the use of Perl-compatible regular expressions.
  • PATTERN: Represents the initial sequence or word you're searching for.
  • \K: Resets the starting point of the reported match. The tool "forgets" any characters matched before this point.
  • TARGET (like \S+ or .*): Specifies what content to capture after the initial PATTERN.

 

Syntax to capture content before a Pattern using grep

When dealing with content preceding a pattern in grep, look-behind assertions come into play. Here's a table for grep that captures content before a specified pattern:

Usage Scenario Command Syntax Description
Word Before Match grep -oP '\S+(?= PATTERN)' Matches the word immediately preceding the PATTERN. (?= PATTERN) is a look-ahead assertion.
Multiple Words Before Match grep -oP '\S+ \S+(?= PATTERN)' Matches the two words immediately preceding the PATTERN. Adjust \S+ repetitions for more words.
Everything Before Match grep -oP '.*(?=PATTERN)' Matches everything from the start of the line to just before the PATTERN.
Specific Characters Before Match grep -oP '.{N}(?=PATTERN)' Captures a specific number of characters (N) before the PATTERN. Replace N with a number.
Non-greedy Matching grep -oP 'STARTPATTERN.*?(?=PATTERN)' Uses non-greedy matching to capture content from a STARTPATTERN to just before an PATTERN.

Key Points to Remember:

  • -o: Outputs only the matched portion of the input.
  • -P: Enables the use of Perl-compatible regular expressions.
  • (?= PATTERN): A look-ahead assertion. It asserts what directly follows the current position in the string but doesn't consume any characters.
  • TARGET (like \S+ or .*): Specifies what content to capture before reaching the PATTERN.

 

Examples - Following a Match with grep:

Here is a table where we demonstrate different examples to grep and print next content:

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Topic Title Command Output
grep and Print After Match echo "I love apples." | grep -oP 'love\K.*' apples.
grep and Print Word After Match echo "Apples are sweet." | grep -oP 'Apples \K\S+' are
grep Word Before Match echo "I love apple pie." | grep -oP '\S+(?= pie)' apple
grep Name Before Price echo "An apple costs $1.25." | grep -oP '\S+(?= costs \$1.25)' apple
grep Word Before 'and' echo "Apple and orange." | grep -oP '\S+(?= and)' Apple
grep Item Before 'is' echo "apple pie is delicious." | grep -oP '\S+(?= is)' pie
bash grep Word Before Match echo "apple is a fruit." | grep -oP '\S+(?= fruit)' a
grep Adjective Before 'apple' echo "The red apple is sweet." | grep -oP '\S+(?= apple)' red
grep and Print Word After Match echo "Apples are very sweet." | grep -oP 'Apples \K\S+' are
grep and Print Next 2 Words After Match echo "Apples are very sweet." | grep -oP 'Apples \K\S+ \S+' are very
grep and Print Next 3 Words After Match echo "Apples are very sweet and juicy." | grep -oP 'Apples \K\S+ \S+ \S+' are very sweet
grep and Print Everything After Match echo "Apples are fruits." | grep -oP 'Apples\K.*' are fruits.

Examples - Preceding a Match with grep:

Here is a table where we demonstrate different examples to grep and print preceding content:

Topic Title Command Output
grep and Print Before Match echo "I love apples." | grep -oP '.*(?= apples)' I love
grep and Print Word Before Match echo "Apples are sweet." | grep -oP '\S+(?= are)' Apples
grep Word Before 'pie' echo "I love apple pie." | grep -oP '\S+(?= pie)' apple
grep Name Before Price echo "An apple costs $1.25." | grep -oP '\S+(?= costs \$1.25)' apple
grep Word Before 'and' echo "Apple and orange." | grep -oP '\S+(?= and)' Apple
grep Item Before 'is' echo "apple pie is delicious." | grep -oP '\S+(?= is)' pie
bash grep Word Before 'fruit' echo "apple is a fruit." | grep -oP '\S+(?= fruit)' a
grep Adjective Before 'apple' echo "The delicious apple is sweet." | grep -oP '\S+(?= apple)' delicious
grep and Print Previous 2 Words Before echo "I really love apple pies." | grep -oP '\S+ \S+(?= pies)' love apple
grep and Print Previous 3 Words Before echo "In summer, I really love apple pies." | grep -oP '\S+ \S+ \S+(?= pies)' really love apple
grep and Print Everything Before Match echo "I love apple pies." | grep -oP '.*(?= pies)' I love apple

 

Awk: A Powerful Text Processing Tool

awk is a versatile text processing tool that can be used to extract data based on patterns. Let's represent the described awk commands in table format:

 

Syntax to capture content after a Pattern using awk

Use awk with the -F flag to specify a delimiter (the pattern), and then print the subsequent field to capture content after the pattern.

Usage Scenario Command Syntax Description
Word After Match awk '/PATTERN/ {print $(NF)}' Prints the last word of lines containing PATTERN.
Multiple Words After Match awk '/PATTERN/ {print $(NF-1), $(NF)}' Prints the last two words of lines containing PATTERN.
Everything After Match awk -F"PATTERN" '{print $2}' Using PATTERN as a field separator and prints everything after it.
Specific Characters After Match Not directly feasible with a simple awk command. Would require more complex string manipulation or a combination with other tools.
Non-greedy Matching Not directly feasible with a simple awk command. Would require more complex string manipulation or a combination with other tools.

 

Syntax to capture content before a Pattern using awk

Use awk with the -F flag to specify a delimiter (the pattern), and then print the preceding field to capture content before the pattern.

Usage Scenario Command Syntax Description
Word Before Match awk '/PATTERN/ {print $(1)}' Prints the first word of lines containing PATTERN.
Multiple Words Before Match awk '/PATTERN/ {print $(1), $(2)}' Prints the first two words of lines containing PATTERN.
Everything Before Match awk -F"PATTERN" '{print $1}' Using PATTERN as a field separator and prints everything before it.
Specific Characters Before Match Not directly feasible with a simple awk command. Would require more complex string manipulation or a combination with other tools.
Non-greedy Matching Not directly feasible with a simple awk command. Would require more complex string manipulation or a combination with other tools.

Key Points to Remember:

  • awk operates primarily on fields and records.
  • The -F option specifies a field separator.
  • $1, $2, ... $(NF) are field variables. $1 refers to the first field, $2 to the second, and so on. $(NF) refers to the last field.
  • More complex scenarios might require you to use awk's string manipulation functions, such as substr, or even combine awk with other tools like grep or sed.

 

Examples - Following a Match with awk:

Topic Title Command Output
awk Print Word After Match echo "I love apples" | awk '/love/{print $3}' apples
awk Find String After Pattern echo "fruits: apples, bananas" | awk -F": " '{print $2}' apples, bananas
awk Print After Match echo "I love: apples" | awk -F": " '/love/{print $2}' apples
awk Print Substring After Match echo "I love apples" | awk '/love/{print substr($3, 2, 4)}' ppl
awk Print String After Match echo "Fruit: Apple" | awk -F": " '/Fruit/{print $2}' Apple
awk Print Characters After Match echo "Color: Blue" | awk -F": " '/Color/{print substr($2, 2, 3)}' Blu
awk Print Line After Match echo -e "Color:\nBlue" | awk '/Color/{getline; print}' Blue
awk Print Everything After Match echo "Color: Blue, Red" | awk -F": " '{print $2}' Blue, Red

 

Examples - Preceding a Match with awk:

Topic Title Command Output
awk Print Word Before Match echo "I love apples" | awk '/apples/{print $2}' love
awk Find String Before Pattern echo "fruits: apples" | awk -F": " '{print $1}' fruits
awk Print Before Match echo "I love: apples" | awk -F": " '/apples/{print $1}' I love
awk Print Substring Before Match echo "I really love apples" | awk '/apples/{print substr($3, 1, 4)}' real
awk Print String Before Match echo "Fruit: Apple" | awk -F": " '/Apple/{print $1}' Fruit
awk Print Characters Before Match echo "Color: Blue" | awk -F": " '/Blue/{print substr($1, 1, 3)}' Col
awk Print Line Before Match echo -e "Color:\nBlue" | awk '/Blue/{getline; print}' Color:
awk Print Everything Before Match echo "Color: Blue, Red" | awk -F"Blue" '{print $1}' Color:

 

Summary

Text manipulation is an integral aspect of data processing, and Bash offers a rich suite of tools to perform these tasks effectively. This article delves deep into the intricacies of commands like grep and awk, elucidating how they can be harnessed to extract specific content following or preceding a match. Through a series of intuitive examples and tables, readers are familiarized with diverse scenarios and command syntaxes. Advanced users will particularly appreciate the section dedicated to combining various tools for complex manipulations, which accentuates the versatility of Bash. Whether you're a beginner aiming to understand the basics or a seasoned user seeking advanced tips, this comprehensive guide ensures you're well-equipped to manipulate text data with finesse in Bash.

 

References

Using grep to get the next WORD after a match in each line
get the next word after grep matching - bash - Stack Overflow
Grep and print only matching word and the next words
Use grep to get next word after match

 

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4 thoughts on “grep & awk regex to print next word after pattern match”

  3. I've log file, it contains java exceptions, need to capture between 2 timestamps, sample log file contents:
22 Apr 2023 01:31:34.051,INFO,[104:ServerService Thread Pool -- 65], xyz, [0],
22 Apr 2023 01:31:34.051,ERROR,[104:ServerService Thread Pool -- 65], xyz, [0],[com.xyz.startup],Exception
       at org.sprinframework etc..................
       at org.sprinframework etc..................
       at org.sprinframework etc..................
22 Apr 2023 01:31:35.067,ERROR,[104:ServerService Thread Pool -- 65], xyz, [0],

    the same above one going to repeat in log files with different timestamps., so, I need a command or script, to capture all lines in between 2 timestamps.
    So, please share,
    Thanks in advance

    Reply

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