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

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 "$ "
}