5 ms·

> So does that mean, that "for" will do something per word of the output of $, rather than per line of output of it? Correct. The argument to "for" is a list o

by sigil 13y ago

> So does that mean, that "for" will do something per word of the output of $, rather than per line of output of it? Correct. The argument to "for" is a list of words. > What to do if I want to do something for every line? Use a while loop. find /some/dir/ -type f | while read -r line; do ; # something with $line done PS. You should almost always use `find` instead of `ls` in shell scripts. Given a pattern, `ls` will exit non-zero if nothing matches it, and you should be treating non-zero exits like you would exceptions in other languages.

joseph 13y ago
One thing to be careful of when doing "while read..." is that a new shell is started on each iteration, so you cannot for example set a variable within the loop that you can use later in the script, as its value will be lost when the shell process exits.
- sigil 13y ago
  > a new shell is started on each iteration This is not actually true. printf "\n\n\n" | while read i; do a="x$a"; echo "$a"; done x xx xxx The accumulator value even carries over after the while loop: printf "\n\n\n" | ( while read i; do a="x$a"; echo "$a"; done ; echo "$a" ) x xx xxx xxx (Technically, whether or not the loop body is executed in a subshell may be implementation dependent. Haven't looked at the POSIX shell spec in a while, but I seem to remember an old ksh that actually used subshells. At any rate, none of the modern sh's and bash force a subshell.) What is true, however, is that a pipeline will execute in a subshell. Maybe that's what you're getting at here, and it is an important caveat. a=y; printf "\n\n\n" | while read i; do a="x$a"; echo "$a"; done; echo "$a" xy xxy xxxy y
  - joseph 13y ago
    Ah, ok. True, when I have had this issue it was after doing something like 'grep "pattern" file | while read ...'. I did not realize it was the pipe that caused this.

by sigil 13y ago

joseph 13y ago

One thing to be careful of when doing "while read..." is that a new shell is started on each iteration, so you cannot for example set a variable within the loop that you can use later in the script, as its value will be lost when the shell process exits.

sigil 13y ago
> a new shell is started on each iteration This is not actually true. printf "\n\n\n" | while read i; do a="x$a"; echo "$a"; done x xx xxx The accumulator value even carries over after the while loop: printf "\n\n\n" | ( while read i; do a="x$a"; echo "$a"; done ; echo "$a" ) x xx xxx xxx (Technically, whether or not the loop body is executed in a subshell may be implementation dependent. Haven't looked at the POSIX shell spec in a while, but I seem to remember an old ksh that actually used subshells. At any rate, none of the modern sh's and bash force a subshell.) What is true, however, is that a pipeline will execute in a subshell. Maybe that's what you're getting at here, and it is an important caveat. a=y; printf "\n\n\n" | while read i; do a="x$a"; echo "$a"; done; echo "$a" xy xxy xxxy y
- joseph 13y ago
  Ah, ok. True, when I have had this issue it was after doing something like 'grep "pattern" file | while read ...'. I did not realize it was the pipe that caused this.