Linux – use expect in shell script

expectlinuxshell

I need to pass two arguments to expect, first one is the command to execute, the second one is the password.

here's my expect.sh

#!/usr/bin/expect
spawn [lrange $argv 0 0]
expect "password:"
send [lindex $argv 1]
interact

main script:

./expect.sh "ssh root@$SERVER1"  $SERVER1_PASS

error:

couldn't execute "{ssh root@xxx.xxx.xx.xxx}": no such file or directory
    while executing
"spawn [lrange $argv 0 0]"
    (file "./expect.sh" line 2)

why?

Best Answer

As far as I can tell, spawn's first argument needs to be a string, not a list of string.

And trying to pass a multi-word command line as a single string is going to cause problems. I think you'd have to split on spaces before calling spawn, and that's going to break if one argument contains a space. Maybe it's better to specify the password as the first argument, and the command as the rest of the arguments.

So try something like:

#!/usr/bin/expect
spawn [lindex $argv 1] [lrange $argv 2 end]
expect "password:"
send [lindex $argv 0]
interact

But then even that doesn't work.

According to Re: expect - spawn fails with argument list on comp.lang.tcl (Google Groups version), we have to call eval to split the list.

So the answer should be:

#!/usr/bin/expect
eval spawn [lrange $argv 1 end]
expect "password:"
send [lindex $argv 0]
interact

Finally, you need to be sending Enter after the password, so you want:

#!/usr/bin/expect
eval spawn [lrange $argv 1 end]
expect "password:"
send [lindex $argv 0]
send '\r'
interact

And then switch the order and don't quote the command when calling it:

./expect.sh "$SERVER1_PASS" ssh root@$SERVER1

But others have already done this. We don't need to re-invent the wheel.

See e.g. expect ssh login script

Related Solutions

Bash – How to check if a directory exists in a Bash shell script

To check if a directory exists in a shell script, you can use the following:

if [ -d "$DIRECTORY" ]; then
  # Control will enter here if $DIRECTORY exists.
fi

Or to check if a directory doesn't exist:

if [ ! -d "$DIRECTORY" ]; then
  # Control will enter here if $DIRECTORY doesn't exist.
fi

However, as Jon Ericson points out, subsequent commands may not work as intended if you do not take into account that a symbolic link to a directory will also pass this check. E.g. running this:

ln -s "$ACTUAL_DIR" "$SYMLINK"
if [ -d "$SYMLINK" ]; then 
  rmdir "$SYMLINK" 
fi

Will produce the error message:

rmdir: failed to remove `symlink': Not a directory

So symbolic links may have to be treated differently, if subsequent commands expect directories:

if [ -d "$LINK_OR_DIR" ]; then 
  if [ -L "$LINK_OR_DIR" ]; then
    # It is a symlink!
    # Symbolic link specific commands go here.
    rm "$LINK_OR_DIR"
  else
    # It's a directory!
    # Directory command goes here.
    rmdir "$LINK_OR_DIR"
  fi
fi

Take particular note of the double-quotes used to wrap the variables. The reason for this is explained by 8jean in another answer.

If the variables contain spaces or other unusual characters it will probably cause the script to fail.

Linux – How to prompt for Yes/No/Cancel input in a Linux shell script

The simplest and most widely available method to get user input at a shell prompt is the read command. The best way to illustrate its use is a simple demonstration:

while true; do
    read -p "Do you wish to install this program?" yn
    case $yn in
        [Yy]* ) make install; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
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done

Another method, pointed out by Steven Huwig, is Bash's select command. Here is the same example using select:

echo "Do you wish to install this program?"
select yn in "Yes" "No"; do
    case $yn in
        Yes ) make install; break;;
        No ) exit;;
    esac
done

With select you don't need to sanitize the input – it displays the available choices, and you type a number corresponding to your choice. It also loops automatically, so there's no need for a while true loop to retry if they give invalid input.

Also, Léa Gris demonstrated a way to make the request language agnostic in her answer. Adapting my first example to better serve multiple languages might look like this:

set -- $(locale LC_MESSAGES)
yesptrn="$1"; noptrn="$2"; yesword="$3"; noword="$4"

while true; do
    read -p "Install (${yesword} / ${noword})? " yn
    if [[ "$yn" =~ $yesexpr ]]; then make install; exit; fi
    if [[ "$yn" =~ $noexpr ]]; then exit; fi
    echo "Answer ${yesword} / ${noword}."
done

Obviously other communication strings remain untranslated here (Install, Answer) which would need to be addressed in a more fully completed translation, but even a partial translation would be helpful in many cases.

Finally, please check out the excellent answer by F. Hauri.

Best Answer

Related Solutions

Bash – How to check if a directory exists in a Bash shell script

Linux – How to prompt for Yes/No/Cancel input in a Linux shell script

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