Strange behavior of shell output file ( Linux )

Question

Do you know why below shell script just generates the output file named 'Loading_EMP.sql' instead of 'Loading_1_EMP.sql'?

#!/bin/bash

JOBID="1"
TABLE="EMP"

echo 'test'  > Loading_$JOBID_$TABLE.sql; 

# Output
Loading_EMP.sql

# Expected Output
Loading_1_EMP.sql

Possible duplicate of [variable interpolation in shell](http://stackoverflow.com/questions/17622106/variable-interpolation-in-shell) — jackrabbit, Jul 30 '16 at 08:07
@jackrabbit : Apart from the variable interpolation issue, there is also an issue of missing double quotes — sjsam, Jul 30 '16 at 08:32

score 3 · Accepted Answer · edited May 23 '17 at 12:08

3

echo 'test'  > Loading_${JOBID}_${TABLE}.sql;

should do it, or better

echo 'test'  > "Loading_${JOBID}_${TABLE}.sql" # to avoid word splitting

In Loading_$JOBID_$TABLE, shell trates $JOBID_ as a single variable and since it is not set, it substitutes $JOBID_ with nothing resulting in Loading_EMP.sql

^{This [ answer ] must read for you.}

edited May 23 '17 at 12:08

Community

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answered Jul 30 '16 at 08:04

sjsam

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I understand that now. Thank you so much! – Sigularity Jul 30 '16 at 08:47
Thanks for accepting the answer, have a great weekend then ;) – sjsam Jul 30 '16 at 08:48

jackrabbit · Answer 2 · 2016-07-30T08:11:36.067

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The interpreter thinks you are referring to a variable named JOBID_. Enclose the name with {}.

echo 'test'  > Loading_${JOBID}_$TABLE.sql

edited Jul 30 '16 at 08:11

answered Jul 30 '16 at 08:04

jackrabbit

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You might consider double quoting `Loading_${JOBID}_$TABLE.sql` to accommodate filenames with spaces. – sjsam Jul 30 '16 at 08:31
Those only matter if you have spaces or other weird characters. His script clearly does not suffer from that. – jackrabbit Jul 30 '16 at 10:25

score 1 · Answer 3 · answered Jul 30 '16 at 08:05

_ is not a special character in shell. So the shell sees this as you echoing a $JOBID_ variable, which is undefined, and thus empty. Instead, you should explicitly show the shell what your variables are by using {}:

echo 'test'  > Loading_${JOBID}_${TABLE}.sql;
# Here -----------------^-----^--^-----^

Strange behavior of shell output file ( Linux )

3 Answers3