Diff for "BashFAQ/021"

How can I replace a string with another string in all files?

sed is a good command to replace strings, e.g.

    sed 's/olddomain\.com/newdomain.com/g' input > output

Note that input and output must differ.

To replace a string in all files of the current directory:

    for i in ./*; do
        sed 's/old/new/g' "$i" > atempfile && mv atempfile "$i"
    done

GNU sed 4.x has a special -i flag which makes the loop and temp file unnecessary:

      sed -i 's/old/new/g' ./*

On some (but not all) BSD systems, sed has a -i flag as well, but it takes a mandatory argument. The above example then becomes

      sed -i '' 's/old/new/g' ./*

which in turn does not work with GNU sed. Effectively, whenever portability matters, sed -i should be avoided.

Those of you who have perl 5 can accomplish the same thing using this code:

    perl -pi -e 's/old/new/g' ./*

Recursively (requires GNU or BSD find):

    find . -type f -print0 | xargs -0 perl -pi -e 's/old/new/g'

If you want to delete lines instead of making substitutions:

    perl -ni -e 'print unless /foo/' ./*
    # Deletes any line containing the perl regex foo

To replace for example all "unsigned" with "unsigned long", if it is not "unsigned int" or "unsigned long" ...:

    find . -type f -print0 | xargs -0 perl -i.bak -pne \
        's/\bunsigned\b(?!\s+(int|short|long|char))/unsigned long/g'

Finally, for those of you with none of the useful things above, here's a script that may be useful:

    #!/bin/sh
    # chtext - change text in several files

    # neither string may contain '|' unquoted
    old='olddomain\.com'
    new='newdomain\.com'

    # if no files were specified on the command line, use all files:
    [ $# -lt 1 ] && set -- ./*

    for file
    do
        [ -f "$file" ] || continue # do not process e.g. directories
        [ -r "$file" ] || continue # cannot read file - ignore it
        # Replace string, write output to temporary file. Terminate script in case of errors
        sed "s|$old|$new|g" -- "$file" > "$file"-new || exit
        # If the file has changed, overwrite original file. Otherwise remove copy
        if cmp -- "$file" "$file"-new >/dev/null 2>&1
        then rm -- "$file"-new              # file has not changed
        else mv -- "$file"-new "$file"      # file has changed: overwrite original file
        fi
    done

If the code above is put into a script file (e.g. chtext), the resulting script can be used to change a text e.g. in all HTML files of the current and all subdirectories:

    find . -type f -name '*.html' -exec chtext {} \;

Many optimizations are possible:

• use another sed separator character than '|', e.g. ^A (ASCII 0x01)

• the find command above could use either xargs or the built-in xargs of POSIX find

Note: set -- ./* in the code above is safe with respect to files whose names contain spaces. The expansion of ./* by set is the same as the expansion done by for, and filenames will be preserved properly as individual parameters, and not broken into words on whitespace.

A more sophisticated example of chtext is here: http://www.shelldorado.com/scripts/cmds/chtext