Diff for "BashFAQ/021"

How can I replace a string with another string in a file, or in all the files in a directory?

ed is the standard UNIX command-based editor. Here are some commonly-used syntaxes for replacing the string olddomain.com by the string newdomain.com in a file named file. All four commands do the same thing, with varying degrees of portability and efficiency:

# Bash
ed -s file <<< $'g/olddomain\\.com/s//newdomain.com/g\nw\nq'

# Bourne (with printf)
printf '%s\n' 'g/olddomain\.com/s//newdomain.com/g' w q | ed -s file

printf 'g/olddomain\\.com/s//newdomain.com/g\nw\nq' | ed -s file

# Bourne (without printf)
ed -s file <<!
g/olddomain\\.com/s//newdomain.com/g
w
q
!

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

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

To do this recursively, the easy way would be to enable globstar in bash 4 (shopt -s globstar, a good idea to put this in your ~/.bashrc) and use:

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

If you don't have bash 4, you can use find. Unfortunately, it's a bit tedious to feed ed stdin for each file hit:

find . -type f -exec bash -c 'printf "%s\n" "g/old/s//new/g" w q | ed -s "$1"' _ {} \;

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 sed (and some BSD seds) 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 ./*              # Other
do
    [ -f "$file" ] &&
        sed 's/old/new/g' "$file" > "$file~" &&
        mv "$file~" "$file"
done

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 your find doesn't have + yet
find . -type f -exec perl -pi -e 's/old/new/g' {} +    # if it does

If you want to delete lines instead of making substitutions:

# Deletes any line containing the perl regex foo
perl -ni -e 'print unless /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 who shun ed and have none of the useful things above, here's a script that may be useful:

# 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 + instead of \; if available

• the chtext script could be replaced with an ed command

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