Loop and Case¶

each line in a variable¶

list=$'One\ntwo\nthree\nfour'
echo "$list"

while IFS= read -r line; do
    echo "... $line ..."
done <<< "$list"

#one line
echo "$list" | while IFS= read -r line; do echo $line; done

while¶

#arithmetic condition
while (( n < m )); do
    ...
    let n++
done

#file system condition
while [ -z "$fn" ]; do
    ...
done

#from input
while read line; do
    process $line
done

#from file
while read line; do
    process $line
done < file.input

#cat to standard output
cat file.input |
while read line; do
    process $line
done

for with count¶

for (( i=0 ; i < 10 ; i++ )); do
    echo $i
done

for (( i=0, j=0 ; i+j < 10 ; i++, j++ )); do
    echo $(( i*j ))
done

for with seq¶

#`$()` runs the command in subshell and
#returns the result with the newlines replaced by whitespace
for v in $(seq 1 .1 1.2) ; do
    echo $v
done

#preferred: can run `seq` in parallel with `while`
seq 1 .1 1.2 |
while read v ; do
    echo $v
done

case¶

;; break
;;& continue matching next patterns

;& fall-through, run next regardless of matching, useful for version patch

case $fn in
    *.gif) gif2jpg $fn
        ;;
    *.tif | *.TIFF) tif2jpg $fn
        ;;
    *) printf "File not supported: %s" $fn
        ;;
esac

case $version in 1.0) update to version 2 ;& #fall-through 2.0) update to version 3 ;& #fall-through *) printf "Nothing to update. It's already the latest version: %s" $version ;; esac ```