Bash command line and input limit

Question

Is there some sort of character limit imposed in bash  or other shells  for how long an input can be  If so  what is that character limit   I e  Is it possible to write a command in bash that is too long for the command line to execute  If there is not a required limit  is there a suggested limit

User · Accepted Answer

The limit for the length of a command line is not imposed by the shell, but by the operating system. This limit is usually in the range of hundred kilobytes. POSIX denotes this limit ARG_MAX and on POSIX conformant systems you can query it with

$ getconf ARG_MAX    # Get argument limit in bytes

E.g. on Cygwin this is 32000, and on the different BSDs and Linux systems I use it is anywhere from 131072 to 2621440.

If you need to process a list of files exceeding this limit, you might want to look at the xargs utility, which calls a program repeatedly with a subset of arguments not exceeding ARG_MAX.

To answer your specific question, yes, it is possible to attempt to run a command with too long an argument list. The shell will error with a message along "argument list too long".

Note that the input to a program (as read on stdin or any other file descriptor) is not limited (only by available program resources). So if your shell script reads a string into a variable, you are not restricted by ARG_MAX. The restriction also does not apply to shell-builtins.

User · Answer

There is a buffer limit of something like 1024   The read will simply hang mid paste or input   To solve this use the -e option   http   linuxcommand org lc3 man pages readh html  -e use Readline to obtain the line in an interactive shell  Change your read to read -e and annoying line input hang goes away

User · Answer

Ok  Denizens  So I have accepted the command line length limits as gospel for quite some time  So  what to do with one s assumptions  Naturally- check them   I have a Fedora 22 machine at my disposal  meaning  Linux with bash4   I have created a directory with 500 000 inodes  files  in it each of 18 characters long  The command line length is 9 500 000 characters  Created thus   seq 1 500000   while read digit  do     touch   printf  abigfilename 06d n   digit   done   And we note      getconf ARG MAX 2097152   Note however I can do this     echo    gt   dev null   But this fails      bin echo    gt   dev null bash   bin echo  Argument list too long   I can run a for loop     for f in    do    done   which is another shell builtin   Careful reading of the documentation for ARG MAX states  Maximum length of argument to the exec functions  This means  Without calling exec  there is no ARG MAX limitation  So it would explain why shell builtins are not restricted by ARG MAX   And indeed  I can ls my directory if my argument list is 109948 files long  or about 2 089 000 characters  give or take   Once I add one more 18-character filename file  though  then I get an Argument list too long error  So ARG MAX is working as advertised  the exec is failing with more than ARG MAX characters on the argument list- including  it should be noted  the environment data

[bash] Bash command line and input limit

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