---

3.7 Control Flow ¶

Because Eshell commands can not (easily) be combined with Lisp forms, Eshell provides command-oriented control flow statements for convenience.

Most of Eshell’s control flow statements accept a conditional. This can take a few different forms. If conditional is a dollar expansion, the condition is satisfied if the result is a non-nil value. Alternately, conditional may be a subcommand, either in command form, e.g. ‘{subcommand}’; or in Lisp form, e.g. ‘(lisp form)’. In that case, the condition is satisfied if the subcommand’s exit status is 0.

if conditional true-subcommand

if conditional true-subcommand else false-subcommand

Evaluate true-subcommand if conditional is satisfied; otherwise, evaluate false-subcommand. Both true-subcommand and false-subcommand should be subcommands, as with conditional.

You can also chain together if/else forms, for example:

if {[ -f file.txt ]} {
 echo found file
} else if {[ -f alternate.txt ]} {
 echo found alternate
} else {
 echo not found!
}

unless conditional false-subcommand

unless conditional false-subcommand else true-subcommand

Evaluate false-subcommand if conditional is not satisfied; otherwise, evaluate true-subcommand. Like above, you can also chain together unless/else forms.

while conditional subcommand

Repeatedly evaluate subcommand so long as conditional is satisfied.

until conditional subcommand

Repeatedly evaluate subcommand until conditional is satisfied.

for var in sequence… subcommand

Iterate over each element of sequence, storing the element in var and evaluating subcommand. If sequence is a range of the form begin..end, iterate over each integer between begin and end, not including end. If sequence is not a sequence, treat it as a list of one element.

If you specify multiple sequences, this will iterate over each of them in turn.

Previous: Remote Access, Up: Commands [Contents][Index]