Searching and Replacing with grep and sed
Unix commands grep and sed can be used to efficiently search and replace strings in a file, a directory, or files acrose multiple directories. Specifically, grep is used to search for a certain string, and sed is used to replace the strings.
Search using grep
grep -l somematchstring somefile.txt
This command searches somematchstring in the file somefile.txt. The option -l means it will print names of files containing matches.
grep -rl somematchstring somedir/
This command searches somematchstring in all files under the directory somedir. The option -l again means it will print names of files containing matches. The option -r means it will go recursively into all subdirectories.
grep -l somematchstring somedir/*.java
This searches somematchstring in all .java files under the directory somedir.
Search and Replace using sed
grep -rl somematchstring somedir/ | xargs sed -i 's/somematchstring/somereplacestring/g'
The grep command will list all files under the directory somedir/ containing somematchstring. The file names are passed on through the pipe ‘|’ delimiter. Then the sed command will replace somematchstring by somereplacestring.
Note that the grep command will pipe only files matching somematchstring to sed. The pipe ‘|’ delimiter is efficient when searching through a lot of files.
The following is another example.
grep -rl 'Windows' ./ | xargs sed -i 's/Windows/Linux/g'
This will search for ‘Windows’ in all files under the current directory, and replace ‘Windows’ by ‘Linux’ for each occurrence ‘Windows’ in each file.