Basic Linux TutorialIntroduction – What is it? Why to learn? Linux installation directory structures Boot process Run levels in Linux Desktop Environments Different shells BASH Internal and External Commands Basic Linux Commands Important files and directories in Linux Environmental and Shell Variables Command history in Linux Character classes in Linux Text editors vim nano Searching files Creating new files Viewing File Contents File commands File permissions and ownership WildCards (Globbing) in files File compression Directory commands xargs command in Linux Comparing files Searching patterns using grep command Translating the characters using tr command Extracting data using cut command Stream editing using sed command Data extraction and reporting using awk command Sorting the file or string input uniq command in Linux Difference between grep, tr, cut, sed and awk commands Hardware commands Hard disk and memory space commands Working with Processes Managing Jobs Working with cron jobs Service command in Linux Network commands Managing Users and Groups Other Popular commands Standard streams and Redirection Pipes Package Managers in Linux
grep command in linux shellgrep command is used to search the pattern in input file or input string. Regular expressions are used to specify the pattern. Here is the syntax of grep command.
To highlight the matches, you can set GREP_OPTIONS variable with below values.
grep <pattern> <filename>
We can use below command to find the pattern “abc” in file f1.txt
To make the search case insensitive, you can use -i switch
grep “abc” f1.txt
To print the line number where match is found, you can use -n switch
grep -i “abc” f1.txt
To print matched line and 3 lines after it, you can use below command
grep -n “abc” f1.txt
To search for the pattern in all files in current directory and all subdirectories, you can use below command.
grep -n -A 3 “abc” f1.txt
To suppress the message saying directories can not be searched, you can use -s switch.
grep -r “abc” *
We can use below command to find all lines not matching the pattern “abc” in file f1.txt. Here -v stands for inverted search.
grep -r -s “abc” *
Some more options on grep are given below.
grep -v “abc” f1.txt
- grep -w “abc” f1 : “-w” option can be used to search for words (not sub strings).
- grep -A 2 “abc” f1 : “-A” option can be used to display n lines after match.
- grep -B 2 “abc” f1 : “-B” option can be used to display n lines before match.
- grep -C 2 “abc” f1 : “-C” option can be used to display n lines before and after match.
- grep -e “term1” -e “term2” : “-e” option is used to search multiple patterns in a file.
- grep -c “abc” f1 : “-c” option is used to print the matches count.
- grep -l “abc” * : “-l” option shows files names that match the pattern. (Instead of matching lines)
- grep -o “xyz.*” f1 : “-o” option is used to print only the matched pattern (instead of whole line)
- grep -n “term” f1 : “-n” option is used to display matching line numbers
egrep commandegrep command is equivalent to “grep -E”. This is also called as extended grep.
fgrep commandfgrep command is equivalent to “grep -F”. This is also called as fast grep.
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