Appendix D. Parsing and Managing Pathnames

#!/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 ${!p//:/}; done }# Filter out empty lines, multiple/trailing slashes, and duplicate entries.function p_filter(){ awk '/^[ ]*$/ {next} {sub(//+$/, "");gsub(//+/, "/")}!x[$0]++' ;}# Rebuild list of items into ':' separated word (PATH-like).function p_build() { paste -sd: ;}# Clean $1 (typically PATH) and rebuild itfunction p_clean(){ local p=${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:echoMYPATH="/bin:/usr/bin/:/bin://bin/" p_append "/project//my project/bin" MYPATHecho "Append '/project//my project/bin' to '/bin:/usr/bin/:/bin://bin/'" echo "(result should be: /bin:/usr/bin:/project/my project/bin)" echo $MYPATHechoMYOTHERPATH="/bin:/usr/bin/:/bin:/project//my project/bin" p_prepend "/project//my project/bin" MYOTHERPATHecho "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 $MYOTHERPATHechop_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 $FOOPATHechoBARPATH="/a:/b/://b c://a:/my local pub" p_clean BARPATHecho "Clean BARPATH='/a:/b/://b c://a:/my local pub'" echo "(result should be: /a:/b:/b c:/my local pub)" echo $BARPATH

Doing it correctly: A quick summaryby David Wheelerhttp://www.dwheeler.com/essays/filenames-in-shell.htmlSo, how can you process filenames correctly in shell? Here's a quicksummary about how to do it correctly, for the impatient who "just want theanswer". In short: Double-quote to use "$variable" instead of $variable,set IFS to just newline and tab, prefix all globs/filenames so they cannotbegin with "-" when expanded, and use one of a few templates that workcorrectly. Here are some of those templates that work correctly: IFS="$(printf '')"  # 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 '')"  controlchars="$(printf '*[01-37177]*')"  for file in $(find . ! -name "$controlchars"') ; do   COMMAND "$file" ... done #  Okay if filenames can't contain tabs or newlines -- #+ beware the assumption. IFS="$(printf '')"  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