BASH create filename form variables

Question

I want to create a filename for redirecting output to.

eg:

ls -lash > $filename

All the variables are set.. So far I've tried the following:

filename=`echo $site . "_location_" . $address . "_" .  $timestamp . ".txt"` 

filename=$site . "_location_" . $address . "_" .  $timestamp . ".txt" 

filename="$site_location_$address_$timestamp.txt"

None have worked.. How do I get a file named like:

site1_location_northeast_071218142325.txt

Thanks

The dot (`.`) is the string concatenation operator in PHP, not in shell script. — axiac, Dec 07 '18 at 14:36
Side note: As answers have pointed out, you don't need command substitution here. When you do though, use the modern form `$(command)` rather than `\`command\``. `$()` is much easier to read and can be conveniently nested. — Soren Bjornstad, Dec 07 '18 at 17:28

chepner · Answer 1 · 2018-12-07T14:42:16.247

2

Just use string interpolation.

filename="${site}_location_${address}_${timestamp}.txt"

The braces prevent the _ from being treated as part of the preceding parameter name (or more precisely, they delimit the enclosed string as the parameter name).

edited Dec 07 '18 at 14:42

answered Dec 07 '18 at 14:35

chepner

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axiac · Accepted Answer · 2018-12-07T14:44:22.960

2

All you need is:

filename="${site}_location_${address}_${timestamp}.txt"

The curly braces around variable names help Bash know you want to replace the value of variables $site and $address. Otherwise, because _ is a valid character in variable names, it thinks you want the use the variables $site_location_ and $address_ (that do not exist.)

edited Dec 07 '18 at 14:44

answered Dec 07 '18 at 14:35

axiac

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Thanks both comments help.. this just had slightly more explanation. – Tom Dec 07 '18 at 14:59

BASH create filename form variables

2 Answers2