Diff for "BashFAQ/021"

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

ed is the standard UNIX command-based editor. Here's three commonly-used syntaxes for replacing the string olddomain.com by the string newdomain.com in a file named file. All three commands do the same although the last two incur the minor additional overhead of a subshell.

    # ed -s file <<< $'s/olddomain\.com/newdomain.com/g\nw'
    # printf '%s\n' 's/olddomain\.com/newdomain.com/g' w | ed -s file
    # printf 's/olddomain\.com/newdomain.com/g\nw' | ed -s file

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

    for file in ./*; do
        ed -s "$file" <<< $'s/old/new/g\nw'
    done

sed is a Stream EDitor, not a file editor. Nevertheless, people everywhere tend to abuse it for trying to edit files. It doesn't edit files. GNU's sed (and some BSD sed's) have a -i option that makes a copy and replaces the original file with the copy. An expensive operation, but if you enjoy unportable code, I/O overhead and bad side effects (such as destroying symlinks), this would be an option:

    # sed -i 's/old/new/g' ./*     # GNU
    # sed -i '' 's/old/new/g' ./*  # BSD
    # for file in ./*; do sed 's/old/new/g' "$file" > "$file"~; mv "$file"~ "$file"; done  # Others

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

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

Recursively using find:

    find . -type f -exec 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 -exec 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

CategoryShell