Shell Script Wildcards – Issues with Output Redirection

bashscriptingshellshell-scriptwildcards

Say I have two scripts:

script1.sh:

#!/bin/bash
version=2.6
log_file="$HOME/log-file-version-$version.log"

touch $log_file &>/dev/null

echo "log to my log file from script 1" >> $HOME/log-file-version-?.?.log

gnome-terminal --tab --active --title="script2" --  sh script2.sh

script2.sh:

#!/bin/bash

echo "log to my log file from script 2" >> $HOME/log-file-version-?.?.log

I run script1.sh.

I'm left with two log files in my home:

log-file-version-2.6.log
log-file-version-?.?.log

log-file-version-2.6.log contains:

log to my log file from script 1

log-file-version-?.?.log contains:

log to my log file from script 2

which means that in script 1 the wildcards from line 7 (>> $HOME/log-file-version-?.?.log) were correctly interpreted, but when a script is run with sh these wildcards don't work.

Why is that and how can I fix this?

I need to use wildcards because I don't want to be passing arguments from shell script to shell script and I want them to be self-sufficient.

I'm using Ubuntu and running these scripts from the default terminal which is gnome-terminal.

Best Answer

The bash manual has this to say in the 3.6 Redirections section:

The word following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic expansion, quote removal, filename expansion, and word splitting. If it expands to more than one word, Bash reports an error.

sh does not do that: from the POSIX shell specification

If the redirection operator is "<<" or "<<-", [...]. For the other redirection operators, the word that follows the redirection operator shall be subjected to tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal. Pathname expansion shall not be performed on the word by a non-interactive shell; an interactive shell may perform it, but shall do so only when the expansion would result in one word.

$ dash
$ echo foo > *
$ ls
'*'  README.md  ...

$ bash
$ echo bar >> *
bash: *: ambiguous redirect

Related Solutions

bash scripting python – How to Have Multiple Possibilities in a Script’s Shebang Line

I'm not expert, but I believe that you shouldn't specify exact python version to use and leave that choice to system/user.

Also you should use that instead of hardcoding path to python in script:

#!/usr/bin/env python

#!/usr/bin/env python3 (or python2)

It is recommended by Python doc in all versions:

A good choice is usually
#!/usr/bin/env python
which searches for the Python interpreter in the whole PATH. However, some Unices may not have the env command, so you may need to hardcode /usr/bin/python as the interpreter path.

In various distributions Python may be installed in different places, so env will search for it in PATH. It should be available in all major Linux distributions and from what I see in FreeBSD.

Script should be executed with that version of Python which is in your PATH and which is chosen by your distribution*.

If your script is compatible with all version of Python except 2.4 you should just check inside of it if it is run in Python 2.4 and print some info and exit.

Footnote

*In Gentoo there is tool called eselect. Using it you may set default versions of different applications (including Python) as default:

$ eselect python list
Available Python interpreters:
  [1]   python2.6
  [2]   python2.7 *
  [3]   python3.2
$ sudo eselect python set 1
$ eselect python list
Available Python interpreters:
  [1]   python2.6 *
  [2]   python2.7
  [3]   python3.2

Shell – In bash, how can I export/set a global variable from a read funtion inside a script, for use in a second script and a config file later on

You can't really. A script can not set an environment variable in the parent shell's environment.

One solution would obviously be to create a third script that runs the two other scripts in the particular way that they need to be run. It would source the first script and then run the second script.

Alternatively, combine the two scripts into one script. If you split them up to "keep things separate", then you can do the same with functions in one and the same script if you wish.

Also,

export name1=$name1

may be shortened to

export name1

Best Answer

Related Solutions

bash scripting python – How to Have Multiple Possibilities in a Script’s Shebang Line

More to read

Footnote

Shell – In bash, how can I export/set a global variable from a read funtion inside a script, for use in a second script and a config file later on

Related Question