Unable to redirect bash output to variable file name

up vote
3
down vote

favorite

I am trying to redirect the bash output to a variable file name. Here is my script looks like

#!/bin/bash
for i in `cat servers`
do
if [ "$i" = "198.162.1.3" ];
then
var="apple"
fi
ssh test@$i "uname -n"
done > /tempout/uname_$var.txt

I am getting the filename as /tempout/uname_.txt

Expected filename should be uname_apple.txt

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

asked Sep 7 at 9:28

xrkr

5814

Don't read lines with for
â€“Â glenn jackman
Sep 7 at 12:47

@glennjackman What makes you think "servers" is a file of lines/records and not just whitespace separated IP addresses?
â€“Â ColleenV
Sep 7 at 13:54

Even if it is, the for i in $(cat file) is wrong. The shell will not only do word splitting (which is the desired effect), it also does filename expansion. set -f is missing.
â€“Â glenn jackman
Sep 7 at 14:27

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to redirect the bash output to a variable file name. Here is my script looks like

#!/bin/bash
for i in `cat servers`
do
if [ "$i" = "198.162.1.3" ];
then
var="apple"
fi
ssh test@$i "uname -n"
done > /tempout/uname_$var.txt

I am getting the filename as /tempout/uname_.txt

Expected filename should be uname_apple.txt

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

asked Sep 7 at 9:28

xrkr

5814

Don't read lines with for
â€“Â glenn jackman
Sep 7 at 12:47

@glennjackman What makes you think "servers" is a file of lines/records and not just whitespace separated IP addresses?
â€“Â ColleenV
Sep 7 at 13:54

Even if it is, the for i in $(cat file) is wrong. The shell will not only do word splitting (which is the desired effect), it also does filename expansion. set -f is missing.
â€“Â glenn jackman
Sep 7 at 14:27

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to redirect the bash output to a variable file name. Here is my script looks like

#!/bin/bash
for i in `cat servers`
do
if [ "$i" = "198.162.1.3" ];
then
var="apple"
fi
ssh test@$i "uname -n"
done > /tempout/uname_$var.txt

I am getting the filename as /tempout/uname_.txt

Expected filename should be uname_apple.txt

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

asked Sep 7 at 9:28

xrkr

5814

I am trying to redirect the bash output to a variable file name. Here is my script looks like

#!/bin/bash
for i in `cat servers`
do
if [ "$i" = "198.162.1.3" ];
then
var="apple"
fi
ssh test@$i "uname -n"
done > /tempout/uname_$var.txt

I am getting the filename as /tempout/uname_.txt

Expected filename should be uname_apple.txt

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

asked Sep 7 at 9:28

xrkr

5814

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

edited Sep 7 at 9:44

Rui F Ribeiro

36.2k1271115

asked Sep 7 at 9:28

xrkr

5814

asked Sep 7 at 9:28

xrkr

5814

asked Sep 7 at 9:28

xrkr

5814

Don't read lines with for
â€“Â glenn jackman
Sep 7 at 12:47

@glennjackman What makes you think "servers" is a file of lines/records and not just whitespace separated IP addresses?
â€“Â ColleenV
Sep 7 at 13:54

Even if it is, the for i in $(cat file) is wrong. The shell will not only do word splitting (which is the desired effect), it also does filename expansion. set -f is missing.
â€“Â glenn jackman
Sep 7 at 14:27

add a commentÂ |Â

Don't read lines with for
â€“Â glenn jackman
Sep 7 at 12:47

@glennjackman What makes you think "servers" is a file of lines/records and not just whitespace separated IP addresses?
â€“Â ColleenV
Sep 7 at 13:54

Even if it is, the for i in $(cat file) is wrong. The shell will not only do word splitting (which is the desired effect), it also does filename expansion. set -f is missing.
â€“Â glenn jackman
Sep 7 at 14:27

Don't read lines with for
â€“Â glenn jackman
Sep 7 at 12:47

@glennjackman What makes you think "servers" is a file of lines/records and not just whitespace separated IP addresses?
â€“Â ColleenV
Sep 7 at 13:54

Even if it is, the for i in $(cat file) is wrong. The shell will not only do word splitting (which is the desired effect), it also does filename expansion. set -f is missing.
â€“Â glenn jackman
Sep 7 at 14:27

add a commentÂ |Â

1 Answer
1

active

oldest

votes

up vote
7
down vote

accepted

The var variable in your code is used before the loop starts to create the output file.

If you want to output the result of the ssh command to a file whose name you construct from $var, then do this:

#!/bin/bash

while read -r server; do
 if [ "$server" = "198.162.1.3" ]; then
 var='apple'
 else
 var='unknown'
 done

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

Here, I've also changed the loop so that it reads the input file line by line (ignoring leading and trailing whitespace on each line), and I've made var get the value unknown if the if statement does not take the "true" branch.

Also, you need -n for ssh. Otherwise, ssh would consume all the available input (here redirected from the servers file).

Another change that could be made is to use case ... esac rather than an if statement, especially if the number of IP addresses that you test for is more than a couple:

#!/bin/bash

while read -r server; do
 case $server in
 198.162.1.3) var=apple ;;
 198.162.1.5) var=cottage ;;
 198.162.1.7) var=bumblebee ;;
 *) var=unknown
 esac

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

1

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

add a commentÂ |Â

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1 Answer
1

active

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1 Answer
1

active

oldest

votes

up vote
7
down vote

accepted

The var variable in your code is used before the loop starts to create the output file.

If you want to output the result of the ssh command to a file whose name you construct from $var, then do this:

#!/bin/bash

while read -r server; do
 if [ "$server" = "198.162.1.3" ]; then
 var='apple'
 else
 var='unknown'
 done

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

Also, you need -n for ssh. Otherwise, ssh would consume all the available input (here redirected from the servers file).

Another change that could be made is to use case ... esac rather than an if statement, especially if the number of IP addresses that you test for is more than a couple:

#!/bin/bash

while read -r server; do
 case $server in
 198.162.1.3) var=apple ;;
 198.162.1.5) var=cottage ;;
 198.162.1.7) var=bumblebee ;;
 *) var=unknown
 esac

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

1

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

add a commentÂ |Â

up vote
7
down vote

accepted

The var variable in your code is used before the loop starts to create the output file.

If you want to output the result of the ssh command to a file whose name you construct from $var, then do this:

#!/bin/bash

while read -r server; do
 if [ "$server" = "198.162.1.3" ]; then
 var='apple'
 else
 var='unknown'
 done

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

Also, you need -n for ssh. Otherwise, ssh would consume all the available input (here redirected from the servers file).

Another change that could be made is to use case ... esac rather than an if statement, especially if the number of IP addresses that you test for is more than a couple:

#!/bin/bash

while read -r server; do
 case $server in
 198.162.1.3) var=apple ;;
 198.162.1.5) var=cottage ;;
 198.162.1.7) var=bumblebee ;;
 *) var=unknown
 esac

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

1

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

add a commentÂ |Â

up vote
7
down vote

accepted

The var variable in your code is used before the loop starts to create the output file.

If you want to output the result of the ssh command to a file whose name you construct from $var, then do this:

#!/bin/bash

while read -r server; do
 if [ "$server" = "198.162.1.3" ]; then
 var='apple'
 else
 var='unknown'
 done

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

Also, you need -n for ssh. Otherwise, ssh would consume all the available input (here redirected from the servers file).

Another change that could be made is to use case ... esac rather than an if statement, especially if the number of IP addresses that you test for is more than a couple:

#!/bin/bash

while read -r server; do
 case $server in
 198.162.1.3) var=apple ;;
 198.162.1.5) var=cottage ;;
 198.162.1.7) var=bumblebee ;;
 *) var=unknown
 esac

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

The var variable in your code is used before the loop starts to create the output file.

If you want to output the result of the ssh command to a file whose name you construct from $var, then do this:

#!/bin/bash

while read -r server; do
 if [ "$server" = "198.162.1.3" ]; then
 var='apple'
 else
 var='unknown'
 done

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

Also, you need -n for ssh. Otherwise, ssh would consume all the available input (here redirected from the servers file).

Another change that could be made is to use case ... esac rather than an if statement, especially if the number of IP addresses that you test for is more than a couple:

#!/bin/bash

while read -r server; do
 case $server in
 198.162.1.3) var=apple ;;
 198.162.1.5) var=cottage ;;
 198.162.1.7) var=bumblebee ;;
 *) var=unknown
 esac

 ssh -n "test@$server" 'uname -n' >"/tempout/uname_$var.txt"
done <servers

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

edited Sep 7 at 15:32

answered Sep 7 at 9:35

Kusalananda

105k14209326

answered Sep 7 at 9:35

Kusalananda

105k14209326

answered Sep 7 at 9:35

Kusalananda

105k14209326

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

1

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

add a commentÂ |Â

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

1

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

Thanks it worked :)
â€“Â xrkr
Sep 7 at 10:09

the input redirection to read is more elegant, but the loop behaves fundamentally different like that. if IP appears in a line together with other words it won't be recognized.
â€“Â Sam
Sep 7 at 10:12

@Sam Yes, the new code expects servers to be a list of IP addresses, one per line.
â€“Â Kusalananda
Sep 7 at 10:32

one per line, with leading and trailing spaces or tabs removed (assuming the default value of $IFS)
â€“Â StÃ©phane Chazelas
Sep 7 at 11:07

add a commentÂ |Â

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