Bash
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==Redirection in bash== | ==Redirection in bash== | ||
Bash's shining moment comes for users who need to see and/or redirect errors to somewhere other than STOUT (your console). Standard input (STIN), standard output (STOUT) and standard error (STERR) are by default sent to the same place: STOUT (on most systems, this will be your console or tty). [[bash]] labels these descriptors 0, 1 and 2, respectively -- you have 10 descriptors, but only 0-2 are actually taken by anything. So | Bash's shining moment comes for users who need to see and/or redirect errors to somewhere other than STOUT (your console). Standard input (STIN), standard output (STOUT) and standard error (STERR) are by default sent to the same place: STOUT (on most systems, this will be your console or tty). [[bash]] labels these descriptors 0, 1 and 2, respectively -- you have 10 descriptors, but only 0-2 are actually taken by anything. So | ||
| − | samizdata# | + | samizdata# myprogram > file |
| − | will send the output of '' | + | will send the output of ''myprogram'' to ''file'' |
| − | samizdata# | + | samizdata# myprogram 2> file |
| − | will send only the '''error''' output of '' | + | will send only the '''error''' output of ''myprogram'' to ''file'' |
| − | samizdata# | + | samizdata# myprogram 2>&1 | command |
will send errors (descriptor 2,) to the same place as output (descriptor 1) and then pipe that to ''command2'' | will send errors (descriptor 2,) to the same place as output (descriptor 1) and then pipe that to ''command2'' | ||
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samizdata# myprogram 1>&2 2>&1 > errors.txt | samizdata# myprogram 1>&2 2>&1 > errors.txt | ||
because when you do the first switch, it's done ''right away'' and when the second >& comes around, it's getting the switched data. This is where the other, normally unused, file descriptors 3-9 come in. You can use them as place-holders, such as: | because when you do the first switch, it's done ''right away'' and when the second >& comes around, it's getting the switched data. This is where the other, normally unused, file descriptors 3-9 come in. You can use them as place-holders, such as: | ||
| − | samizdata# | + | samizdata# myprogram 3>&2 2>&1 1>&3 | command |
| − | will make 3 point to the same place as 2, 2 point to 1, and finally, 1 point to 3 | + | will make the output of ''myprogram'' do this: 3 point to the same place as 2, 2 point to 1, and finally, 1 point to 3 and then pipe all of it to ''command'' |
Seen [[bash]]'s [[man]] page for more info. | Seen [[bash]]'s [[man]] page for more info. | ||
Revision as of 23:34, 29 August 2004
The Bourne Again Shell (located in /bin/bash) is the default shell of the Linux operating system and is the shell that users of that system will likely be most familiar with.
Redirection in bash
Bash's shining moment comes for users who need to see and/or redirect errors to somewhere other than STOUT (your console). Standard input (STIN), standard output (STOUT) and standard error (STERR) are by default sent to the same place: STOUT (on most systems, this will be your console or tty). bash labels these descriptors 0, 1 and 2, respectively -- you have 10 descriptors, but only 0-2 are actually taken by anything. So
samizdata# myprogram > file
will send the output of myprogram to file
samizdata# myprogram 2> file
will send only the error output of myprogram to file
samizdata# myprogram 2>&1 | command
will send errors (descriptor 2,) to the same place as output (descriptor 1) and then pipe that to command2
Okay, let's say you want to send output to your screen and errors to a file. You can't just do
samizdata# myprogram 1>&2 2>&1 > errors.txt
because when you do the first switch, it's done right away and when the second >& comes around, it's getting the switched data. This is where the other, normally unused, file descriptors 3-9 come in. You can use them as place-holders, such as:
samizdata# myprogram 3>&2 2>&1 1>&3 | command
will make the output of myprogram do this: 3 point to the same place as 2, 2 point to 1, and finally, 1 point to 3 and then pipe all of it to command
Seen bash's man page for more info.
Note: Bash is not available by default in the base system, but can easily be installed from ports if desired.
Other shells that you can install and customize for ease of use are the bash, tcsh, psh, ksh, zsh.
see also: bash homepage
