Question

I’m trying some staff that is working perfectly when I write it in the regular shell, but when I include it in a bash script file, it doesn’t.
First example:

m=`date +%m`
m_1=$((m-1))
echo $m_1

This gives me the value of the last month (actual minus one), but doesn’t work if its executed from a script.

Second example:

m=6
m=$m"t"
echo m

This returns “6t” in the shell (concatenates $m with “t”), but just gives me “t” when executing from a script.

I assume all these may be answered easily by an experienced Linux user, but I’m just learning as I go.

Thanks in advance.

Answer 1

Re-check your syntax.

Your first code snippet works either from command line, from bash and from sh since your syntax is valid sh. In my opinion you probably have typos in your script file:

~$ m=`date +%m`; m_1=$((m-1)); echo $m_1
4
~$ cat > foo.sh
m=`date +%m`; m_1=$((m-1)); echo $m_1
^C
~$ bash foo.sh
4
~$ sh foo.sh
4

The same can apply to the other snippet with corrections:

~$ m=6; m=$m"t"; echo $m
6t
~$ cat > foo.sh
m=6; m=$m"t"; echo $m
^C
~$ bash foo.sh
6t
~$ sh foo.sh
6t