This is an example of parsing and transforming filenames and, in
particular, pathnames. It draws heavily on the functionality of
sed.
#!/usr/bin/env bash #----------------------------------------------------------- # Management of PATH, LD_LIBRARY_PATH, MANPATH variables... # By Emmanuel Rouat <no-email> # (Inspired by the bash documentation 'pathfuncs' and on # discussions found on stackoverflow: # http://stackoverflow.com/questions/370047/ # http://stackoverflow.com/questions/273909/#346860 ) # Last modified: Sat Sep 22 12:01:55 CEST 2012 # # The following functions handle spaces correctly. # These functions belong in .bash_profile rather than in # .bashrc, I guess. # # The modular aspect of these functions should make it easy # to expand them to handle path substitutions instead # of path removal etc.... # # See http://www.catonmat.net/blog/awk-one-liners-explained-part-two/ # (item 43) for an explanation of the 'duplicate-entries' removal # (it's a nice trick!) #-----------------------------------------------------------
# Show $@ (usually PATH) as list. function p_show() { local p="$@" && for p; do [[ ${!p} ]] && echo -e ${!p//:/\\n}; done }
# Filter out empty lines, multiple/trailing slashes, and duplicate entries. function p_filter() { awk '/^[ \t]*$/ {next} {sub(/\/+$/, "");gsub(/\/+/, "/")}!x[$0]++' ;}
# Rebuild list of items into ':' separated word (PATH-like). function p_build() { paste -sd: ;}
# Clean $1 (typically PATH) and rebuild it function p_clean() { local p=${1} && eval ${p}='$(p_show ${p} | p_filter | p_build)' ;}
# Remove $1 from $2 (found on stackoverflow, with modifications). function p_rm() { local d=$(echo $1 | p_filter) p=${2} && eval ${p}='$(p_show ${p} | p_filter | grep -xv "${d}" | p_build)' ;}
# Same as previous, but filters on a pattern (dangerous... #+ don't use 'bin' or '/' as pattern!). function p_rmpat() { local d=$(echo $1 | p_filter) p=${2} && eval ${p}='$(p_show ${p} | p_filter | grep -v "${d}" | p_build)' ;}
# Delete $1 from $2 and append it cleanly. function p_append() { local d=$(echo $1 | p_filter) p=${2} && p_rm "${d}" ${p} && eval ${p}='$(p_show ${p} d | p_build)' ;}
# Delete $1 from $2 and prepend it cleanly. function p_prepend() { local d=$(echo $1 | p_filter) p=${2} && p_rm "${d}" ${p} && eval ${p}='$(p_show d ${p} | p_build)' ;}
# Some tests: echo MYPATH="/bin:/usr/bin/:/bin://bin/" p_append "/project//my project/bin" MYPATH echo "Append '/project//my project/bin' to '/bin:/usr/bin/:/bin://bin/'" echo "(result should be: /bin:/usr/bin:/project/my project/bin)" echo $MYPATH
echo MYOTHERPATH="/bin:/usr/bin/:/bin:/project//my project/bin" p_prepend "/project//my project/bin" MYOTHERPATH echo "Prepend '/project//my project/bin' \ to '/bin:/usr/bin/:/bin:/project//my project/bin/'" echo "(result should be: /project/my project/bin:/bin:/usr/bin)" echo $MYOTHERPATH
echo p_prepend "/project//my project/bin" FOOPATH # FOOPATH doesn't exist. echo "Prepend '/project//my project/bin' to an unset variable" echo "(result should be: /project/my project/bin)" echo $FOOPATH
echo BARPATH="/a:/b/://b c://a:/my local pub" p_clean BARPATH echo "Clean BARPATH='/a:/b/://b c://a:/my local pub'" echo "(result should be: /a:/b:/b c:/my local pub)" echo $BARPATH
How can you process filenames correctly in shell?
Doing it correctly: A quick summary by David Wheeler http://www.dwheeler.com/essays/filenames-in-shell.html
So, how can you process filenames correctly in shell? Here's a quick summary about how to do it correctly, for the impatient who "just want the answer". In short: Double-quote to use "$variable" instead of $variable, set IFS to just newline and tab, prefix all globs/filenames so they cannot begin with "-" when expanded, and use one of a few templates that work correctly. Here are some of those templates that work correctly:
IFS="$(printf '\n\t')" # Remove SPACE, so filenames with spaces work well.
# Correct glob use: #+ always use "for" loop, prefix glob, check for existence: for file in ./* ; do # Use "./*" ... NEVER bare "*" ... if [ -e "$file" ] ; then # Make sure it isn't an empty match. COMMAND ... "$file" ... fi done
# Correct glob use, but requires nonstandard bash extension. shopt -s nullglob # Bash extension, #+ so that empty glob matches will work. for file in ./* ; do # Use "./*", NEVER bare "*" COMMAND ... "$file" ... done
# These handle all filenames correctly; #+ can be unwieldy if COMMAND is large: find ... -exec COMMAND... {} \; find ... -exec COMMAND... {} \+ # If multiple files are okay for COMMAND.
# This skips filenames with control characters #+ (including tab and newline). IFS="$(printf '\n\t')" controlchars="$(printf '*[\001-\037\177]*')" for file in $(find . ! -name "$controlchars"') ; do COMMAND "$file" ... done
# Okay if filenames can't contain tabs or newlines -- #+ beware the assumption. IFS="$(printf '\n\t')" for file in $(find .) ; do COMMAND "$file" ... done
# Requires nonstandard but common extensions in find and xargs: find . -print0 | xargs -0 COMMAND
# Requires nonstandard extensions to find and to shell (bash works). # variables might not stay set once the loop ends: find . -print0 | while IFS="" read -r -d "" file ; do ... COMMAND "$file" # Use quoted "$file", not $file, everywhere. done
# Requires nonstandard extensions to find and to shell (bash works). # Underlying system must include named pipes (FIFOs) #+ or the /dev/fd mechanism. # In this version, variables *do* stay set after the loop ends, # and you can read from stdin. #+ (Change the 4 to another number if fd 4 is needed.)
while IFS="" read -r -d "" file <&4 ; do COMMAND "$file" # Use quoted "$file" -- not $file, everywhere. done 4< <(find . -print0)
# Named pipe version. # Requires nonstandard extensions to find and to shell's read (bash ok). # Underlying system must include named pipes (FIFOs). # Again, in this version, variables *do* stay set after the loop ends, # and you can read from stdin. # (Change the 4 to something else if fd 4 needed).
mkfifo mypipe
find . -print0 > mypipe & while IFS="" read -r -d "" file <&4 ; do COMMAND "$file" # Use quoted "$file", not $file, everywhere. done 4< mypipe