This question already has answers here:
Difference between single and double quotes in Bash
(7 answers)
Closed 2 years ago.
This is MyScript.sh
I want to execute a script as a text inside my script, I have tried to do it like so:
bash -c "
#!/bin/bash
STR=6
echo $STR
"
Prints empty line.
I tried replacing bash -c with sh -c or eval, all options acts the same, why is that and how can it be solved?
Using single quotes to avoid interpretation in the current shell:
$ cat myscript.sh
bash -c 'STR=6; echo $STR'
./myscript.sh
6
Related
This question already has answers here:
Difference between single and double quotes in Bash
(7 answers)
Closed 2 years ago.
A)
first I run export a=1&&echo $a in linux terminal and I get 1.
[root#ip-172-31-16-92 ec2-user]# export a=1&&echo $a
1
B)
But when I run sh -c "export a=2&&echo $a" and I still get 1 instead of 2.
[root#ip-172-31-16-92 ec2-user]# sh -c "export a=2&&echo $a"
1
What happend? If sh -c "export a=2&&echo $a" itself is a child process of the terminal,it should have its own environment, first it should make a copy of his father environment,so a=1,but when it execute export a=2 ,environment a should be set to 2,then echo $a should be 2.But it returns 1,what happend?
Try this one and and you'll see it works.
sh -c 'export a=2&&echo $a'
When enclosed in double-quotes, $a is expanded to its current value by the shell before invoking sh.
This question already has answers here:
Usage of expect command within a heredoc
(1 answer)
Pass commands as input to another command (su, ssh, sh, etc)
(3 answers)
Closed 4 years ago.
I have a script that I need to execute through ssh as another use, is there a way to pass whole script like this:
ssh -t user#server.com sudo -u user2 sh -c << EOF
cd /home
ls
dir=$(pwd)
echo "$dir"
echo "hello"
....
EOF
Returns: sh: -c: option requires an argument
ssh'ing and sudo'ing separately is not an option and putting .sh file directly on the machine is not possible.
sh -c requires a command string as the argument. Since you are reading the commands from standard input (through heredoc), you need to use sh -s option:
ssh -t user#server.com sudo -u user2 sh -s << 'EOF'
cd /home
ls
dir=$(pwd)
echo "$dir"
echo "hello"
...
EOF
From man sh:
-c
string If the -c option is present, then commands are read from string. If there are arguments after the string, they are assigned to the positional parameters, starting with $0.
-s
If the -s option is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell.
Need to quote the heredoc marker to prevent the parent shell from interpreting the content.
This question already has answers here:
is it possible to use variables in remote ssh command?
(2 answers)
Closed 6 years ago.
I am trying to execute some shell script on a remote server via SSH.
Given below is a code sample:
ssh -i $KEYFILE_PATH ubuntu#$TARGET_INSTANCE_IP "bash" << EOF
#!/bin/bash
cat /home/ubuntu/temp.txt
string=$(cat /home/ubuntu/temp.txt )
echo $string
EOF
cat prints the expected result but
$string prints nothing.
How do I store the return value of cat in a variable?
You need to make the content of Here doc literal otherwise they will be expanded in the current shell, not in the desired remote shell.
Quote EOF:
ssh .... <<'EOF'
...
...
EOF
You should be able to simply do this:
ssh -i $KEYFILE_PATH ubuntu#$TARGET_INSTANCE_IP "bash" <<'_END_'
cat /home/ubuntu/temp.txt
string=$(cat /home/ubuntu/temp.txt)
echo $string
_END_
<<'_END_' ... _END_ is called a Here Document literal, or "heredoc" literal. The single quotes around '_END_' prevent the local shell from interpreting variables and commands inside the heredoc.
The intermediate shell is not required (assuming you use bash on the remote system).
Also you dont have to use an intermediate HERE-DOC. Just pass a multiline Command:
ssh -i $KEYFILE_PATH ubuntu#$TARGET_INSTANCE_IP '
cat /home/ubuntu/temp.txt
string=$(cat /home/ubuntu/temp.txt )
echo $string
'
Note I am using single quotes to prevent evaluation on the local shell.
This question already has answers here:
Why does shell ignore quoting characters in arguments passed to it through variables? [duplicate]
(3 answers)
Closed 6 years ago.
I'm trying to write a database call from within a bash script and I'm having problems with a sub-shell stripping my quotes away.
This is the bones of what I am doing.
#---------------------------------------------
#! /bin/bash
export COMMAND='psql ${DB_NAME} -F , -t --no-align -c "${SQL}" -o ${EXPORT_FILE} 2>&1'
PSQL_RETURN=`${COMMAND}`
#---------------------------------------------
If I use an 'echo' to print out the ${COMMAND} variable the output looks fine:
echo ${COMMAND}
screen output:-
#---------------
psql drupal7 -F , -t --no-align -c "SELECT DISTINCT hostname FROM accesslog;" -o /DRUPAL/INTERFACES/EXPORTS/ip_list.dat 2>&1
#---------------
Also if I cut and paste this screen output it executes just fine.
However, when I try to execute the command as a variable within a sub-shell call, it gives an error message.
The error is from the psql client to the effect that the quotes have been removed from around the ${SQL} string.
The error suggests psql is trying to interpret the terms in the sql string as parameters.
So it seems the string and quotes are composed correctly but the quotes around the ${SQL} variable/string are being interpreted by the sub-shell during the execution call from the main script.
I've tried to escape them using various methods: \", \\", \\\", "", \"" '"', \'"\', ... ...
As you can see from my 'try it all' approach I am no expert and it's driving me mad.
Any help would be greatly appreciated.
Charlie101
Instead of storing command in a string var better to use BASH array here:
cmd=(psql ${DB_NAME} -F , -t --no-align -c "${SQL}" -o "${EXPORT_FILE}")
PSQL_RETURN=$( "${cmd[#]}" 2>&1 )
Rather than evaluating the contents of a string, why not use a function?
call_psql() {
# optional, if variables are already defined in global scope
DB_NAME="$1"
SQL="$2"
EXPORT_FILE="$3"
psql "$DB_NAME" -F , -t --no-align -c "$SQL" -o "$EXPORT_FILE" 2>&1
}
then you can just call your function like:
PSQL_RETURN=$(call_psql "$DB_NAME" "$SQL" "$EXPORT_FILE")
It's entirely up to you how elaborate you make the function. You might like to check for the correct number of arguments (using something like (( $# == 3 ))) before calling the psql command.
Alternatively, perhaps you'd prefer just to make it as short as possible:
call_psql() { psql "$1" -F , -t --no-align -c "$2" -o "$3" 2>&1; }
In order to capture the command that is being executed for debugging purposes, you can use set -x in your script. This will the contents of the function including the expanded variables when the function (or any other command) is called. You can switch this behaviour off using set +x, or if you want it on for the whole duration of the script you can change the shebang to #!/bin/bash -x. This saves you explicitly echoing throughout your script to find out what commands are being run; you can just turn on set -x for a section.
A very simple example script using the shebang method:
#!/bin/bash -x
ec() {
echo "$1"
}
var=$(ec 2)
Running this script, either directly after making it executable or calling it with bash -x, gives:
++ ec 2
++ echo 2
+ var=2
Removing the -x from the shebang or the invocation results in the script running silently.
This question already has answers here:
How to cat <<EOF >> a file containing code?
(5 answers)
Closed 7 years ago.
I'm trying to run a bash script that ssh's onto a remote host and stops the single docker container that is running.
#!/usr/bin/env bash
set -e
ssh <machine> <<EOF
container=$(docker ps | awk 'NR==2' | awk '{print $1;}')
docker stop $container
EOF
However, I get the following error:
stop.sh: line 4: docker: command not found
When I do this manually (ssh to the machine, run the commands) all is fine, but when trying to do so by means of a script I get the error. I guess that my command substitution syntax is incorrect and I've searched and tried all kinds of quotes etc but to no avail.
Can anyone point me to where I'm going wrong?
Use <<'EOF' (or <<\EOF -- quoting only the first character will have the same effect) when starting your heredoc to prevent its expansions from being evaluated locally.
BTW, personally, I'd write this a bit differently:
#!/bin/sh -e
ssh "$1" bash <<'EOF'
{ read; read container _; } < <(docker ps)
docker stop "$container"
EOF
The first read consumes the first line of docker ps output; the second extracts only the first column -- using bash builtins only.