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This is what the until loop is for: until some_command do sleep 1 done It is the logical negation of a while loop. The spec says: The until Loop The until loop shall continuously execute one comp …

if ls -A1q ./somedir/ | grep -q . then ! echo somedir is not empty else echo somedir is empty fi The above is a POSIX-compatible test - and should be very fast. ls will list all files/dirs in a …

opt() case ${1##*:*}:${#2} in (--:*) ! x=$((x-2)) ;; (-nonfileoption:[!0]*) p=;; (-fileoption:[!0]*) p=\$2/;; (*:0) eval $"{$x"':?Bad option::arg: "$1::$2"}';; (*) ev …

To do as asked you need only change += to =. Rather than appending to an existing value for every true case found, if you overwrite the last true case with a new one each time then when the loop ends …

Another noteworthy quality about "$*" and "$@" is that they represent the shell array - the current set of the shell's arguments. These are changeable with the set built-in, but are more generally the …

_fn() { set -- "$@" $(cat) while ${1+:} false ; do echo "$1" && [ "$1" = "arg2" ] && echo "$1" $YOUR_CHK shift done } echo "arg2" | _fn "arg1" OUTPUT arg1 arg2 arg …

Your shell can handle bitwise ops, though, for any serious processing, it's going to be awfully slow, and it can't handle anything more than say 20 or so digits at a time. Still: sh <<\CMD print …

set -- ./aaa_bbb_ccc_ddd_[!ul]* cp "$@" -t $location2 var=$*

rand=$(tr -dc '[:lower:]' </dev/urandom | dd bs=1 count=1 status=none) until [ "$in" = "$rand" ] && echo "correct" ; do in=$(stty raw dd bs=1 count=1 status=none </dev/tty stty sane …

find . -type f -iname "readme.txt" -exec sh -c ' for f do ls -1qap ${f%/*} | grep -v "\(readme.txt\$\|/\$\|.\{1,2\}\$\)" && echo rm "$f" ; done' \{\} +

f=IGNORE_NAMES_20140606-2014-06-06.txt mv "$f" "${f%%-*}.txt"

It would be far better if you didn't use echo at all. The use of echo when combined with arbitrary input can have unintended effects. What's more, you do not need wc to count the characters in a shell …

Basically you're trying to set '$trimfilename' to 'Connectivity' when you do: if '$trimfilename'='Connectivity'... if - when in command position - is not a command in the same sense that echo and e …

With dd you can reliably read a single byte from a file. With stty you can set a min number of bytes to qualify a terminal read and a time out in tenths of a second. Combine those two and you can do w …

cd -P . for dir in ./*/ do cd -P "$dir" ||continue printf %s\\n "$PWD" >&2 command && cd "$OLDPWD" || ! break; done || ! cd - >&2 The above command doesn't need to do any subshells - it just …