How to find if a file exists in expect script

Question

I have a statement inside my expect script like this

send "sed -i -e 's/$oldport/$newport/' backup.txt\r"
expect "$ "

However I wish to first check whether the file backup.txt exist and if it does, then edit it.

How do I acheive this?

Thanks

Answer 1

Here is a quick approach by using ls

set file "backup.txt"
send "ls $file\r"
expect {
        "\r\n$file" {puts "\nfile exists"}
        "cannot access $file" {puts "\nfile not found"}
}

You can just replace puts "\nfile exists" with your statement.

Answer 2

Since expect is an extension of Tcl, all Tcl commands are available to use:

if {[file exists backup.txt]} {
    send "sed -i -e 's/$oldport/$newport/' backup.txt\r"
    expect "$ "
}