Comments on: Wizard Boot Camp, Part Three: Using Standard I/O from Shells

By: dbolivar

dbolivar — Tue, 30 Nov 1999 00:00:00 +0000

Great article, very useful information not only for shell scripts, but also to deeply understand the standard I/O. Thanks.

By: santoshbr4

santoshbr4 — Tue, 30 Nov 1999 00:00:00 +0000

Highly informative. A worthy effort. Thank you for sharing your knowledge.

By: beerse

beerse — Tue, 30 Nov 1999 00:00:00 +0000

Nice composition. Some things things to add: The above is (as far as I can see) based on bourne-shell and deriviants like ksh, bash and such. The c-shell (and deriviants like tcsh) have a different aproach on how stdio is handled. My experience tells that I prefer the bourne-shell in scripting and the c-shell on the commandline.

There is a page on ‘useless use of cat’ (just google for that). As far as I remember is it using stdio.

By: dford

dford — Tue, 30 Nov 1999 00:00:00 +0000

A ‘definitely not to be missed’ series – Thank you
- David

By: bros

bros — Tue, 30 Nov 1999 00:00:00 +0000

Hey Jerry

the “exec

By: bros

bros — Tue, 30 Nov 1999 00:00:00 +0000

Hey Jerry

the exec with afile as stdin trick doesn't work for me
it seems that exec it trying to execute the
lines of afile and fails (bash 3.2.25)...

just FYI :)

anyways, great article...thanks.

By: sharder

sharder — Tue, 30 Nov 1999 00:00:00 +0000

Hi,

Thanks for a really great article. These are things I really need, and have not been able to learn anywhere else.

I have the same problem as 'bros' with GNU bash, version 3.00.16(1): the 'exec

By: sharder

sharder — Tue, 30 Nov 1999 00:00:00 +0000

Hi,

Thanks for a really great article. These are things I really need, and have not been able to learn anywhere else.

I have the same problem as 'bros' with GNU bash, version 3.00.16(1): the 'exec [from] afile' reads afile as a list of commands (and closes the terminal when finished).

[and again same problem as 'bros' the editor is not happy about the left-arrow "[from]" sign]

By: lexfiend

lexfiend — Tue, 30 Nov 1999 00:00:00 +0000

@bros/Soren:

I can confirm that the exec redirection script that you both have problems with works exactly as advertised under bash 3.2.25 and 2.05b (well, once you've corrected /etc/passed to /etc/passwd, of course).

On the off-chance that it's being run under a non-Bourne shell, as Corne pointed out, try prefixing your script with the line:

#!/bin/sh

If that doesn't work, post the actual error message you see.

By: oldache

oldache — Tue, 30 Nov 1999 00:00:00 +0000

Thank you, Jerry.
When we review the command mode, we always understand something new, like in Literature when we read a good book once more.

By: isabellf

isabellf — Tue, 30 Nov 1999 00:00:00 +0000

Whoever complained about the so called lack of wizardry in the first installment of the series : keep quiet now !

Good work.

By: allenhalsey

allenhalsey — Tue, 30 Nov 1999 00:00:00 +0000

Great article! Thanks!

@bros/Soren: I experience the same problem with my bash 2.05b.0.

The following does work and demonstrates the principle being described:

cat afile | (ls afile; rm afile; ls afile; head -1)

However, the head command on my system causes STDIN to stop flowing; i.e.:

cat afile | (head -1; head -1)

only returns 1 line:

daemon:x:1:1:Owner of many system processes:/usr/sbin:/bin/sh

A workaround is to replace each 'head -1' with 'read line; echo "$line"'

Allen

By: djeepp

djeepp — Tue, 30 Nov 1999 00:00:00 +0000

We put our daemons right inside the inittab (poor practice, I know) and I always wondered about that mysterious 2>$1 on all of them. This really clears it up.

By: djeepp

djeepp — Tue, 30 Nov 1999 00:00:00 +0000

Oops, I mean 2>&1.