Table of Contents
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 initialPATTERN
.
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 thePATTERN
.
Examples - Following a Match with grep
:
Here is a table where we demonstrate different examples to grep and print next content:
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 assubstr
, or even combineawk
with other tools likegrep
orsed
.
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
Related Keywords: awk print word after match, grep after match, grep word after match, awk find string after pattern, awk print after match, grep next word after match, bash get word after match, awk print substring after match, grep everything after match, awk print string after match, awk print characters after match, awk print line after match, awk print everything after match, grep print after match, grep string after match, grep get word after match, grep print word after match, bash grep after match, bash print everything after match, grep text after match
Fantastic… Countless hours saved… This post should be top on Google.. Thank you
Priceless! Thank you!
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
You can try