'shell script ambiguous redirect [duplicate]

I am trying to create simple shell script which will identify difference between output of two text files. I am able to successfully run script when I redirect to file (i.e. > a and > b).

What I am trying below is to redirect output to variable instead of file to avoid unnecessary file creation but I am getting error ambiguous redirect.

Can someone educate me how to fix this error? 

    sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" | awk '{print $1, $2}' > $a
    sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/last/msmscgatewaylast |grep "CIMD2:" |awk '{print $1, $2}'  > $b
    echo="diff $a $b"

#echo "$DIFF"

test2.sh: line 2: $b: ambiguous redirect

I have also tried other way but get different error

$a=`sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" |awk '{print $1, $2}'`
$b=`sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/last/msmscgatewaylast |grep "CIMD2:"|awk '{print $1, $2}'`
echo="diff <$a <$b"

test1.sh: line 1: =CSMSH3: command not found test1.sh: line 2: =CSMSH3: command not found

But individual commands are working fine when executed from shell prompt

"sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" |awk '{print $1, $2}'"

also tried below from command prompt but fails in script

diff <(sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" |awk '{print $1, $2}') <(sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/last/msmscgatewaylast |grep "CIMD2:" |awk '{print $1, $2}') get below error test4.sh: line 1: syntax error near unexpected token `('

shellredirectambiguous


Solution 1:[1]

You can do it using command substitution

foo=$(sed 'bar' baz.txt)

or process substitution

read foo < <(sed 'bar' baz.txt)

or with Bash 4.2 you can use lastpipe

shopt -s lastpipe
sed 'bar' baz.txt | read foo

Solution 2:[2]

Your:

sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" | awk {print $1, $2}' > $a
sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/last/msmscgatewaylast |grep "CIMD2:" |awk '{print $1, $2}'  > $b

should really be:

a=$(sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/msmscgateway |grep "CIMD2:" | awk '{print $1, $2}')
b=$(sed -n '/eTopUp MU(55) Gateway Status1:/,/eTopUp MU(60) Gateway Status:/p' /root/scripts/last/msmscgatewaylast |grep "CIMD2:" |awk '{print $1, $2}')

To put the output into variables. Right now it probably complains because $a and $b in your case translates to nothing when it expands.

However as someone mentions, this probably won't work with diff $a $b.

Solution 3:[3]

No need for variables at all if you don't want to (in Bash at least):

diff <(echo -e "a\nb\nc") <(echo -e "a\nc\nc")

Basic syntax is

diff <(CMD1) <(CMD2)

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Zombo
Solution 2 Jite
Solution 3 Kjell Andreassen

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