I'm passing a variable to a script on the command line. What is the character limit of a command? eg:
$ MyScript reallyreallyreally...reallyreallyreallylongoption
Thanks.
Server Fault is a question and answer site for system and network administrators. It only takes a minute to sign up.
Sign up to join this communityI'm passing a variable to a script on the command line. What is the character limit of a command? eg:
$ MyScript reallyreallyreally...reallyreallyreallylongoption
Thanks.
The shell/OS imposed limit is usually one or two hundred thousand characters.
getconf ARG_MAX
will give you the maximum input limit for a command. On the Debian system I currently have a terminal open on this returns 131072
which is 128*1024
. The limit is reduced by your environment variables and if my memory serves me correctly these are passed in the same structure by the shell, though that will only take off a few hundred characters in most cases. To find an approximation of this value run env | wc -c
- this suggests 325 characters at the current time on this login on this machine.
Scripts are likely to permit this full length, but it is not unlikely that other utilities will impose their own limits either intentionally or through design issues. There may also be artificial limits to how long an individual argument on a long command line can be, and/or how long a path to a file can be.
getconf ARG_MAX
gives 2097152, but the max arg length I can pass is still 131071 (and I don't have to deduct the size of the environment).
– Dennis Williamson
Jul 23 '10 at 14:10
xargs
and even find -exec
are your friends when dealing with giant argument lists.
– coredump
Jul 23 '10 at 14:15
getconf
is kernel level I think. Perhaps bash is setting a lower limit by its design/configuration? Also, my knowledge of this comes from some time ago so it could be that things have changed a little recently, though it isn't an area I'd expect to see a lot of movement in except in new experimental shells.
– David Spillett
Jul 23 '10 at 19:07
ksh
, zsh
, dash
, fish
and Bash 3 as I did in Bash 4. The error message from fish
may be informative: "fish: The total size of the argument and environment lists (130kB) exceeds the operating system limit of 2.0MB." However, set | wc -c
is 306317 and env | wc -c
is 2507 which don't account for the difference. I don't know what else is being counted.
– Dennis Williamson
Jul 23 '10 at 22:02
ARG_MAX indeed limits the total size of the command line and the environment, but you're facing an additional limitation: one argument must not be longer than MAX_ARG_STRLEN (which is unfortunately hard-coded to be 131072).
Do you mean what is the longest variable length? To figure that out you can use perl's "x" to create a very long variable name:
VAR=`perl -e 'print "a"x131071'` ; bash a.sh $VAR
On My system 131071 works:
and the variable is printed at 131072 it's too big:
VAR=`perl -e 'print "a"x131072'` ; bash a.sh $VAR
bash: /bin/bash: Argument list too long
perl
and a script: /bin/echo "$(printf "%*s" 131071 ".")">/dev/null
– Dennis Williamson
Jul 23 '10 at 14:13
printf '%s\n' "$(printf '%*s' 131072 .)" >/dev/null
works.
– jarno
Sep 24 '17 at 5:24
printf
is a shell built-in, so bash
does not need to do an exec()
for spawning another process. ARG_MAX
only matters to the length of the argument list of the exec
functions (exec()
, execl()
, execlp()
, execvp()
, execvpe()
, etc.).
– Vincent Olivert Riera
Jul 3 '19 at 10:04
echo $(python -c "print('.' * 100000000)")
on Ubuntu 19.10. – Boris Mar 30 '20 at 19:39