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.
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Sign up to join this communityThe 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).
Jul 23, 2010 at 14:10
xargs
and even find -exec
are your friends when dealing with giant argument lists.
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.
Jul 23, 2010 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.
Jul 23, 2010 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).
MAX_ARG_STRLEN
has been based on current stack size limits since around 2011. Try ulimit -S -s unlimited
before trying to execute a very long command line. Note that sudo
will overwrite your limits so you cannot run very long sudo ...
even after setting stack size.
Nov 2, 2021 at 11:03
MAX_ARG_STRLEN
being a hard-coded constant in latest Linux. Maybe you're thinking ARG_MAX
?
ARG_MAX
because it defines the command line and size of the environment and scales automatically according to current stack. The MAX_ARG_STRLEN
is hardcoded as you wrote and doesn't usually cause problems.
Jan 2, 2022 at 21:08
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
Jul 23, 2010 at 14:13
printf '%s\n' "$(printf '%*s' 131072 .)" >/dev/null
works.
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.).
Jul 3, 2019 at 10:04
xargs
provides another method to get detailed information on command line length limit, including the theoretical maximum for your system, the usable maximum, the minimum specified by POSIX and the current buffer size limit.
You do this by providing no input to xargs
and providing the option --show-limits
. The man page also recommends providing the --no-run-if-empty
option (a GNU extension).
Example Use/Output
$ xargs --no-run-if-empty --show-limits </dev/null
Your environment variables take up 3643 bytes
POSIX upper limit on argument length (this system): 2091461
POSIX smallest allowable upper limit on argument length (all systems): 4096
Maximum length of command we could actually use: 2087818
Size of command buffer we are actually using: 131072
Maximum parallelism (--max-procs must be no greater): 2147483647
echo $(python -c "print('.' * 100000000)")
on Ubuntu 19.10.echo
is a builtin. Try/bin/echo $(python -c "print('.' * 100000000)")
and you will get something likebash: /bin/echo: Argument list too long