Gerbil Scheme

Shell Command Support

The :std/cli/shell library provides facilities for working with Unix shell code

usage

(import :std/cli/shell)

An earlier version of this library used to be available as :clan/shell in gerbil-utils.

Interface

easy-shell-character?

(easy-shell-character? character) => bool

Returns true if the character if a string may contain the character in any position without that this fact requiring the string to be quoted in any shell. This include alphanumeric characters and those in "%+,-./:=@_" (not including the double quotes).

All other ASCII characters may require the string to be quoted in some circumstances. For good measure we also quote strings containing non-ASCII characters.

Examples:

> (string-for-each (lambda (c) (or (easy-shell-character? c) (error "foo")))
    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789@%+,-./:=@_") ;; no error
> (string-for-each (lambda (c) (or (not (easy-shell-character? c)) (error "foo")))
    "!`~#$^&*()[{]}\\|;'\"<>? \r\n\t\v") ;; no error either

needs-shell-escape?

(needs-shell-escape? string) => bool

Returns true if the string contains any character known or suspected to sometimes or always require quoting in any Unix shell.

The current implementation only trusts strings where every character satisfies easy-shell-character? to not require quoting.

Examples:

> (andmap needs-shell-escape? ["foo?" "~user" "$1" "*.*" "!1" "ab\\cd" "{}" "a;b" "&amp;" "|" "a b  c"])
#t
> (ormap needs-shell-escape? ["foo" "%-_=+:,./" "1" "..." "abcd" "x=y:z,t.z/u+v_w"])
#f

escape-shell-token

(escape-shell-token string) => shell-escaped-string

Given a string, returns a shell-escaped-string that, when included in a Unix shell command, will expand into the input string.

Examples:

> (map escape-shell-token ["foo?" "~user" "$1" "*.*" "!1" "ab\\cd" "{}" "a;b" "&amp;" "|" "a b  c"])
("\"foo?\"" "\"~user\"" "\"\\$1\"" "\"*.*\"" "\"!1\"" "\"ab\\\\cd\"" "\"{}\"" "\"a;b\"" "\"&amp;\"" "\"|\"" "\"a b  c\"")
> (let (l ["foo" "%-_=+:,./" "1" "..." "abcd" "x=y:z,t.z/u+v_w"])
    (equal? l (map escape-shell-token l)))
#t

->envvar

(->envvar . str) => environment-variable-name

Given a list of arguments str, return a string to be used as a shell environment variable name following the convention of having only upper-case ASCII letters and digits and underscores.

The arguments are passed to as-string then uppercased, and any non-empty sequence of characters other than letters and digits are replaced by a single underscore.

Examples:

> (->envvar "foo")
"FOO"
> (->envvar "bar baz")
"BAR_BAZ"
> (->envvar '("bar " "+!@#$") #(#\@ #\! "#") "baz")
"BAR_BAZ"

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