This started as a post about shell arrays as means of maintaining filenames with spaces in them. Sadly, it fails at that. Still, compare two shell constructs:<\/p>\n\n\n\n
$ egrep -li 'icon' $(find ~\/src -type f -name '*.py' | egrep -v venv)<\/code><\/code><\/pre>\n\n\n\nAgainst:<\/p>\n\n\n\n
$ set -A python_files $(find ~\/src -type f -name '*.py' | egrep -v venv)\n$ for f in ${python_files[@]}; do egrep -li icon \"${f}\"; done<\/code><\/pre>\n\n\n\nNote well that the second construct preserves whitespacing in filenames even if one where foolish enough to create a python program with whitespace in it’s filename.<\/p>\n\n\n\n
I find myself doing the former a lot and there are a few places in my source code tree where there are embedded spaces in a directory. It’s probably time to retrain my finger memory to use the latter construct. This post comes because I find myself revisiting things occasionally. When people start with Unix, a common question is what’s the difference between $*<\/code>, $@<\/code>, \"$*\"<\/code>, and \"$@\"<\/code>? This isn’t original work but here’s a shell script that answers the question.<\/p>\n\n\n\n$ cat foo.sh\n#! \/bin\/bash\n\necho \"## \"'$*' -- expands elements\nfor arg in $*; do\n echo \"\\\"${arg}\\\"\"\ndone\necho \n\necho \"## \"'$@' -- expands elements\nfor arg in $@; do\n echo \"\\\"${arg}\\\"\"\ndone\necho \n\necho \"## \"'\"$*\"' -- all elements\nfor arg in \"$*\"; do\n echo \"\\\"${arg}\\\"\"\ndone\necho \n\necho \"## \"'\"$@\"'-- expands elements maintaining whitespace\nfor arg in \"$@\"; do\n echo \"\\\"${arg}\\\"\"\ndone\necho \n\nexit 0\n<\/code><\/pre>\n\n\n\nhere’s what you get when you run the code:<\/p>\n\n\n\n
$ \/bin\/bash foo.sh one two 'three four' five\n## $* -- expands elements\n\"one\"\n\"two\"\n\"three\"\n\"four\"\n\"five\"\n\n## $@ -- expands elements\n\"one\"\n\"two\"\n\"three\"\n\"four\"\n\"five\"\n\n## \"$*\" -- all elements\n\"one two three four five\"\n\n## \"$@\"-- expands elements maintaining whitespace\n\"one\"\n\"two\"\n\"three four\"\n\"five\"\n\n$ <\/code><\/pre>\n\n\n\nWith arrays things are slightly different:<\/p>\n\n\n\n
#! \/bin\/bash\n\n## If Korn Shell -- set -A list \"$@\" also works\n\nlist=( \"$@\" )\n\necho \"length: ........... ${#list[@]}\"\necho \"all elements: ..... ${list[@]}\"\necho\n\nfor arg in \"${list[@]}\"; do\n echo \"\\\"${arg}\\\"\"\ndone\necho\n\nexit 0\n<\/code><\/pre>\n\n\n\nAnd the output when you run it:<\/p>\n\n\n\n
$ \/bin\/ksh foo.sh one two 'three four' five\nlength: ........... 4\nall elements: ..... one two three four five\n\n\"one\"\n\"two\"\n\"three four\"\n\"five\"\n\n$ \/bin\/bash foo.sh one two 'three four' five\nlength: ........... 4\nall elements: ..... one two three four five\n\n\"one\"\n\"two\"\n\"three four\"\n\"five\"\n\n(venv) $ output<\/code><\/pre>\n\n\n\nAs above, sadly once you pipe the output of this into another program, in this case egrep -v ...<\/code> to throw away the python that was pulled into your virtual environment, the spacis seems to get lost. Maybe some python can fix this?<\/p>\n","protected":false},"excerpt":{"rendered":"This started as a post about shell arrays as means of maintaining filenames with spaces in them. Sadly, it fails at that. Still, compare two shell constructs: Against: Note well that the second construct preserves whitespacing in filenames even if one where foolish enough to create a python program with whitespace in it’s filename. I … <\/p>\n