How to concatenate two strings into one string in B-shell?

jimmyjiang · 01-07-2008, 11:23 AM

hi,
I have trouble to put 2 string together.what I need is a date format like:Jan 7 09

so I wrote a small script:

#!/bin/sh
v1= date |cut -d " " --fields=2,3,4
echo $v1

v2= date |cut -d " " --fields=5 |cut -d: -f1
echo $v2

v3 = ${v1} ${v2}
echo $v3

the output is:
[root@96742-migoi8 ~]# ./maillog.sh
Jan 7

12

./maillog.sh: line 9: v3: command not found

what 's wrong with my script?
thanks in advance!
jimmy

colucix · 01-07-2008, 01:03 PM

Well... there are some issues in your script. Let's see...

Code:

#!/bin/sh
v1= date |cut -d " " --fields=2,3,4
echo $v1

1. when assigning variables you should not put any blank space around the sign =.
2. to assign the output of a command to a variable (command substitution) you have to use the proper syntax. In the Bourne shell /bin/sh, this is done by sourronding the command with back ticks, as in `command`. In the Bourne Again shell /bin/bash, you can use also the syntax $(command). So these first lines will be:

Code:

#!/bin/sh
v1=`date | cut -d " " --fields=2,3,4`
echo $v1

The same apply to the second part

Code:

v2=`date | cut -d " " --fields=5 | cut -d: -f1`
echo $v2

3. to do string concatenation you have to put together the originating strings (as you already tried to do), but again don't leave any space around the sign =. Furthermore, if you want a blank space between the two strings you should use double quotes:

Code:

v3="$v1 $v2"
echo $v3

Just a note: to debug scripts you can run using

Code:

sh -x script.sh

or bash -x if using the Bourne Again shell. This will give you a trace of all the commands executed by the shell, together with the variable or command substitutions.

jimmyjiang · 01-07-2008, 02:36 PM

thanks, it works! but has one prolbem, how can I make 2 space btwn "Jan" and "7"? I tried:v3="$v1 $v2", but not work.

colucix · 01-07-2008, 04:35 PM

You can preserve multiple spaces by quoting the variable:

Code:

v1=hello
v2=world
v3="$v1       $v2"
echo $v3            # output: hello world
echo "$v3"          # output: hello       world

jimmyjiang · 01-08-2008, 11:18 AM

it works great. thanks a lot!

colucix · 01-08-2008, 01:15 PM

You're welcome! Just a side note: you can obtain the same result using "format specification" in the command "date", e.g.

Code:

$ date +"%b %e  %H"
Jan  8  20

See man date for the various format specifications. Also look careful at the spaces and extra characters inside the quotes. For examples the following are valid formats, but give different results:

Code:

date +"%b %e  %H"
date +"%b%e%H"
date +"%b, day = %e  hour = %H"