This question is somewhat related to the question I asked here, but it has not been adequately answered. What interests me here is the following:
When I run the command type -t test on a remote computer, I get the answer 'function' because the 'test' is an existing function inside the .bashrc file on the remote computer.
However, when I run this SSH command on the local computer,
s="$(
ssh -T $HOST <<'EOSSH'
VAR=$(type -f test)
echo $VAR
EOSSH
)"
echo $s
I don't get anything printed. The first question would be how do I make this work?
The second question builds on the previous one. That is, my ultimate goal is to define on a local computer which function I want to check on a remote computer and come up with an adequate answer, ie.:
a="test"
s="$(
ssh -T $HOST <<'EOSSH'
VAR=$(type -f $a)
echo $VAR
EOSSH
)"
echo $s
So, I would like the variable s to be equal to 'function'. How to do it?
how do I make this work?
Either load .bashrc (. .bashrc) or start an interactive session (bash -i).
Because your work is not-interactive, if you want .bashrc loaded and it has no protection against non-interactive use, just load it. If not, maybe move your function somewhere else, to something you can source. If not, be prepared that interactive session may print /etc/motd and /etc/issue and other interactive stuff.
Remove -T - you do not need a tty for non-interactive work.
I would like the variable s to be equal to 'function'. How to do it?
I recommend using declare to transfer all the work and context that you need, which is flexible and works generically, preserves STDIN and doesn't require you to deal with the intricacies escaping inside a here document. Specifically request bash shell from the remote and use printf "%q" to properly escape all the data.
functions_to_check=(a b c)
fn_exists() { [[ "$(LC_ALL=C type -t -- "$1" 2>/dev/null)" = function ]]; }
work() {
for f in "${functions_to_check[#]}"; do
if fn_exists "$f"; then
echo "Great - function $f exists!"
else
echo "Och nuu - no function $f!"
fi
done
}
ssh "$host" "$(printf "%q " bash -c "
$(declare -p function_to_check) # transfer variables
$(declare -f fn_exists work) # transfer functions
work # run the work to do
")"
Related
I have the following shell script. The purpose is to loop thru each line of the target file (whose path is the input parameter to the script) and do work against each line. Now, it seems only work with the very first line in the target file and stops after that line got processed. Is there anything wrong with my script?
#!/bin/bash
# SCRIPT: do.sh
# PURPOSE: loop thru the targets
FILENAME=$1
count=0
echo "proceed with $FILENAME"
while read LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done < $FILENAME
echo "\ntotal $count targets"
In do_work.sh, I run a couple of ssh commands.
The problem is that do_work.sh runs ssh commands and by default ssh reads from stdin which is your input file. As a result, you only see the first line processed, because the command consumes the rest of the file and your while loop terminates.
This happens not just for ssh, but for any command that reads stdin, including mplayer, ffmpeg, HandBrakeCLI, httpie, brew install, and more.
To prevent this, pass the -n option to your ssh command to make it read from /dev/null instead of stdin. Other commands have similar flags, or you can universally use < /dev/null.
A very simple and robust workaround is to change the file descriptor from which the read command receives input.
This is accomplished by two modifications: the -u argument to read, and the redirection operator for < $FILENAME.
In BASH, the default file descriptor values (i.e. values for -u in read) are:
0 = stdin
1 = stdout
2 = stderr
So just choose some other unused file descriptor, like 9 just for fun.
Thus, the following would be the workaround:
while read -u 9 LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done 9< $FILENAME
Notice the two modifications:
read becomes read -u 9
< $FILENAME becomes 9< $FILENAME
As a best practice, I do this for all while loops I write in BASH.
If you have nested loops using read, use a different file descriptor for each one (9,8,7,...).
More generally, a workaround which isn't specific to ssh is to redirect standard input for any command which might otherwise consume the while loop's input.
while read -r line; do
((count++))
echo "$count $line"
sh ./do_work.sh "$line" </dev/null
done < "$filename"
The addition of </dev/null is the crucial point here, though the corrected quoting is also somewhat important for robustness; see also When to wrap quotes around a shell variable?. You will want to use read -r unless you specifically require the slightly odd legacy behavior you get for backslashes in the input without -r. Finally, avoid upper case for your private variables.
Another workaround of sorts which is somewhat specific to ssh is to make sure any ssh command has its standard input tied up, e.g. by changing
ssh otherhost some commands here
to instead read the commands from a here document, which conveniently (for this particular scenario) ties up the standard input of ssh for the commands:
ssh otherhost <<'____HERE'
some commands here
____HERE
ssh -n option prevents checking the exit status of ssh when using HEREdoc while piping output to another program.
So use of /dev/null as stdin is preferred.
#!/bin/bash
while read ONELINE ; do
ssh ubuntu#host_xyz </dev/null <<EOF 2>&1 | filter_pgm
echo "Hi, $ONELINE. You come here often?"
process_response_pgm
EOF
if [ ${PIPESTATUS[0]} -ne 0 ] ; then
echo "aborting loop"
exit ${PIPESTATUS[0]}
fi
done << input_list.txt
This was happening to me because I had set -e and a grep in a loop was returning with no output (which gives a non-zero error code).
I have the following shell script. The purpose is to loop thru each line of the target file (whose path is the input parameter to the script) and do work against each line. Now, it seems only work with the very first line in the target file and stops after that line got processed. Is there anything wrong with my script?
#!/bin/bash
# SCRIPT: do.sh
# PURPOSE: loop thru the targets
FILENAME=$1
count=0
echo "proceed with $FILENAME"
while read LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done < $FILENAME
echo "\ntotal $count targets"
In do_work.sh, I run a couple of ssh commands.
The problem is that do_work.sh runs ssh commands and by default ssh reads from stdin which is your input file. As a result, you only see the first line processed, because the command consumes the rest of the file and your while loop terminates.
This happens not just for ssh, but for any command that reads stdin, including mplayer, ffmpeg, HandBrakeCLI, httpie, brew install, and more.
To prevent this, pass the -n option to your ssh command to make it read from /dev/null instead of stdin. Other commands have similar flags, or you can universally use < /dev/null.
A very simple and robust workaround is to change the file descriptor from which the read command receives input.
This is accomplished by two modifications: the -u argument to read, and the redirection operator for < $FILENAME.
In BASH, the default file descriptor values (i.e. values for -u in read) are:
0 = stdin
1 = stdout
2 = stderr
So just choose some other unused file descriptor, like 9 just for fun.
Thus, the following would be the workaround:
while read -u 9 LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done 9< $FILENAME
Notice the two modifications:
read becomes read -u 9
< $FILENAME becomes 9< $FILENAME
As a best practice, I do this for all while loops I write in BASH.
If you have nested loops using read, use a different file descriptor for each one (9,8,7,...).
More generally, a workaround which isn't specific to ssh is to redirect standard input for any command which might otherwise consume the while loop's input.
while read -r line; do
((count++))
echo "$count $line"
sh ./do_work.sh "$line" </dev/null
done < "$filename"
The addition of </dev/null is the crucial point here, though the corrected quoting is also somewhat important for robustness; see also When to wrap quotes around a shell variable?. You will want to use read -r unless you specifically require the slightly odd legacy behavior you get for backslashes in the input without -r. Finally, avoid upper case for your private variables.
Another workaround of sorts which is somewhat specific to ssh is to make sure any ssh command has its standard input tied up, e.g. by changing
ssh otherhost some commands here
to instead read the commands from a here document, which conveniently (for this particular scenario) ties up the standard input of ssh for the commands:
ssh otherhost <<'____HERE'
some commands here
____HERE
ssh -n option prevents checking the exit status of ssh when using HEREdoc while piping output to another program.
So use of /dev/null as stdin is preferred.
#!/bin/bash
while read ONELINE ; do
ssh ubuntu#host_xyz </dev/null <<EOF 2>&1 | filter_pgm
echo "Hi, $ONELINE. You come here often?"
process_response_pgm
EOF
if [ ${PIPESTATUS[0]} -ne 0 ] ; then
echo "aborting loop"
exit ${PIPESTATUS[0]}
fi
done << input_list.txt
This was happening to me because I had set -e and a grep in a loop was returning with no output (which gives a non-zero error code).
I have the following shell script. The purpose is to loop thru each line of the target file (whose path is the input parameter to the script) and do work against each line. Now, it seems only work with the very first line in the target file and stops after that line got processed. Is there anything wrong with my script?
#!/bin/bash
# SCRIPT: do.sh
# PURPOSE: loop thru the targets
FILENAME=$1
count=0
echo "proceed with $FILENAME"
while read LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done < $FILENAME
echo "\ntotal $count targets"
In do_work.sh, I run a couple of ssh commands.
The problem is that do_work.sh runs ssh commands and by default ssh reads from stdin which is your input file. As a result, you only see the first line processed, because the command consumes the rest of the file and your while loop terminates.
This happens not just for ssh, but for any command that reads stdin, including mplayer, ffmpeg, HandBrakeCLI, httpie, brew install, and more.
To prevent this, pass the -n option to your ssh command to make it read from /dev/null instead of stdin. Other commands have similar flags, or you can universally use < /dev/null.
A very simple and robust workaround is to change the file descriptor from which the read command receives input.
This is accomplished by two modifications: the -u argument to read, and the redirection operator for < $FILENAME.
In BASH, the default file descriptor values (i.e. values for -u in read) are:
0 = stdin
1 = stdout
2 = stderr
So just choose some other unused file descriptor, like 9 just for fun.
Thus, the following would be the workaround:
while read -u 9 LINE; do
let count++
echo "$count $LINE"
sh ./do_work.sh $LINE
done 9< $FILENAME
Notice the two modifications:
read becomes read -u 9
< $FILENAME becomes 9< $FILENAME
As a best practice, I do this for all while loops I write in BASH.
If you have nested loops using read, use a different file descriptor for each one (9,8,7,...).
More generally, a workaround which isn't specific to ssh is to redirect standard input for any command which might otherwise consume the while loop's input.
while read -r line; do
((count++))
echo "$count $line"
sh ./do_work.sh "$line" </dev/null
done < "$filename"
The addition of </dev/null is the crucial point here, though the corrected quoting is also somewhat important for robustness; see also When to wrap quotes around a shell variable?. You will want to use read -r unless you specifically require the slightly odd legacy behavior you get for backslashes in the input without -r. Finally, avoid upper case for your private variables.
Another workaround of sorts which is somewhat specific to ssh is to make sure any ssh command has its standard input tied up, e.g. by changing
ssh otherhost some commands here
to instead read the commands from a here document, which conveniently (for this particular scenario) ties up the standard input of ssh for the commands:
ssh otherhost <<'____HERE'
some commands here
____HERE
ssh -n option prevents checking the exit status of ssh when using HEREdoc while piping output to another program.
So use of /dev/null as stdin is preferred.
#!/bin/bash
while read ONELINE ; do
ssh ubuntu#host_xyz </dev/null <<EOF 2>&1 | filter_pgm
echo "Hi, $ONELINE. You come here often?"
process_response_pgm
EOF
if [ ${PIPESTATUS[0]} -ne 0 ] ; then
echo "aborting loop"
exit ${PIPESTATUS[0]}
fi
done << input_list.txt
This was happening to me because I had set -e and a grep in a loop was returning with no output (which gives a non-zero error code).
I have a list of IP addresses, and my end goal is to ssh into each one, and reset them one-at-a-time. I was asked to use Linux / Bash, which I am not extremely familiar. My code right now will take the first IP from the list, and connect to it, but it never moves on past that point. I believe the issue is somewhere between the while read oneip3 and do code. Any help is greatly appreciated.
The way I run this script is as follows: (I have a list of IP addresses in a separate text file):
./runscript.txt ip_list.txt
while read oneip3
do
(sleep 5
echo "yes\r"
sleep 3
echo -e "password\r"
sleep 3
echo -e "reset\r"
sleep 3
echo -e "yes\r"
sleep 20
echo -e "\r"
) | ssh -t -t -oHostKeyAlgorithms=+ssh-dss admin#$oneip3
done < $1
You didn't provide SSH argument. So it opens an interactive shell.
It is a good reason to be stuck on the first machine (maybe there is other reason...)
Try this to debug
... | ssh -t -t -oHostKeyAlgorithms=+ssh-dss "admin#$oneip3" pwd
Other remarks in comment about StrictHostKeyChecking seams good too (if you are really concern by security, you can deploy all needed keys by hand firstly)
I have a bash function which takes an array as an argument and it executes multiple commands.
Based on user input I want to run all the commands in this method locally or on remote machine. It has many quotes in the commands and echoing with "" will become ugly.
This is how I am invoking the function right now:
run_tool_commands "${ARGS[#]}"
function run_tool_commands {
ARGS=("$#")
.. Loads of commands here
}
if [ case 1 ]; then
# run locally
else
# run remotely
fi
This seems helpful, but this is possible if I have the method text piped to "here document".
If
all the commands that are to be executed under run_tool_commands are present on remote system as well,
All commands are executables, & not alias/functions
All these excutables are in default paths. (No need to source .bashrc or any other file on remote.)
Then perhaps this code may work: (not tested):
{ declare -f run_tool_commands; echo run_tool_commands "${ARGS[#]}"; } | ssh -t user#host
OR
{ declare -f run_tool_commands;
echo -n run_tool_commands;
for arg in "${ARGS[#]}"; do
echo -ne "\"$t\" ";
done; } | ssh -t user#host
Using for loop, to preserve quotes around arguments. (may or may not be required, not tested.)