Using a bash function from a script

Question

What is the right way of assigning the output of lowercase_last2 to another variable? What am I doing wrong below?

I have a shell script test_lowercase_last.sh that defines a couple of functions

#!/bin/bash

function lowercase_last2() (
    PART2=/"${1##*/}"
    PART1=${1%"$PART2"}
    PART2_LOWER=$(echo "$PART2" | tr '[:upper:]' '[:lower:]')
    echo ${PART1}${PART2_LOWER}
)

function basic() (
    echo "Testing"
)

and another script that means to use them

#!/bin/bash
echo $(basic)
echo $(lowercase_last /home/santiago/Test)

But this is what I get

$ source test_lowercase_last.sh
$ ./test_bash_func.sh
./test_bash_func.sh: line 2: basic: command not found

./test_bash_func.sh: line 3: lowercase_last: command not found

I actually mean to assign the output of lowercase_last2 to another variable, but I guess once I get this right, it should be straightforward. Then the question.

Sourcing functions into your interactive shell doesn't export them to child processes unless you do that explicitly. Which is good; you wouldn't want interactive-shell customization to be able to break random scripts that you run. — Charles Duffy
– Charles Duffy, Commented Apr 17, 2020 at 15:47
...so, the right thing is to source the library with the functions in the script that needs those functions. — Charles Duffy
– Charles Duffy, Commented Apr 17, 2020 at 15:48
BTW, using a .sh extension on a library that's using deliberately POSIX-noncompliant syntax is misleading at best. function foo() { is merging the legacy-ksh function foo { syntax and the POSIX-compliant foo() { syntax in a way that's not compatible with either legacy ksh or the POSIX specification. — Charles Duffy
– Charles Duffy, Commented Apr 17, 2020 at 15:49
...if you write a shell library that uses bash-only syntax, name it with a .bash extension. Whereas executables (a category including shell scripts as opposed to shell libraries) should have no extension at all; you run pip, not pip.py; and you run ls, not ls.elf. — Charles Duffy
– Charles Duffy, Commented Apr 17, 2020 at 15:50
@CharlesDuffy - As for the mixing of legacy-ksh and POSIX, what changes would you suggest I introduce? — sancho.s ReinstateMonicaCellio
– sancho.s ReinstateMonicaCellio, Commented Apr 17, 2020 at 19:18

Charles Duffy · Accepted Answer · 2020-04-17 15:51:34Z

2

Source the library in the script you use it from:

#!/bin/bash
source test_lowercase_last.sh

echo "$(basic)"
echo "$(lowercase_last /home/santiago/Test)"

Unless you use export -f lowercase_last basic to export your functions to the environment, they are not automatically inherited by separate shells. (Subshells inherit copies of internal state; but those are fork()ed with no exec() call; when you run a new script, it's across an exec boundary, so it doesn't have access to the original process's non-exported variables).

By the way -- see BashPitfalls #14 re: why echo's arguments should always be quoted when non-constant (and, as an aside, the last table in https://wiki.bash-hackers.org/scripting/obsolete discussing function declaration syntax options).

answered Apr 17, 2020 at 15:51

Charles Duffy

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2 Comments

sancho.s ReinstateMonicaCellio Over a year ago

I actually mean to source test_lowercase_last.sh in .bashrc, so the functions are available in all child processes. So I would add line export -f lowercase_last basic in my script, as you suggested... (I am not certain the export is needed in this case, I will check).

Charles Duffy Over a year ago

Writing a script that doesn't work on anyone's account but yours, or after a sudo execution that discards environment variables, or after running a non-bash shell that (legally!) discards environment variables that don't translate to valid shell variable names, isn't exactly a principle-of-least-surprise practice.

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