Zsh – Parameter Expansion Techniques

variable substitutionzsh

I tried to display the content of the variable fpath in column form using parameter expansion, and I couldn't do it.

After some trying and web browsing I just found another solution; which does exactly what I want. It is:

print -C1 $fpath

But I still wonder how to do it the other way. The closest I got was:

echo ${fpath//' '/'\n'}

But I fail to identify the white space character, so the '\n' substitution never takes place. I tried to no avail:

echo ${fpath// /'\n'}
echo ${fpath//'\t'/'\n'}

I wonder, out of curiosity, what I am doing wrong.

Best Answer

fpath is an array. You should not try to demote it to a string and then replace characters in it with newlines.

With ksh-like array expansion syntax:

$ printf '%s\n' "${fpath[@]}"
/usr/local/share/zsh/site-functions
/usr/share/zsh/site-functions
/usr/share/zsh/5.7.1/functions

With zsh, you can also use "$fpath[@]" or "${(@)fpath}".

You can also do:

$ printf '%s\n' $fpath
/usr/local/share/zsh/site-functions
/usr/share/zsh/site-functions
/usr/share/zsh/5.7.1/functions

But note that it skips empty elements of the array (likely not a problem for $fpath).

zsh's print builtin can also print elements one per line with the -l option. Like in ksh where the print builtin comes from, you do need the -r option though to print arbitrary data raw, so:

print -rl -- $fpath

would be equivalent to the standard printf '%s\n'.

They differ from -C1 when $fpath is an empty list in which case print -rC1 -- $fpath outputs nothing while print -rl and printf '%s\n' output one empty line, so

print -rC1 -- "$array[@]"

is probably the closest to what you want to print elements of the array one per line which in bash/ksh you could write:

[ "${#array[@]}" -eq 0 ] || printf '%s\n' "${array[@]}"

Related Solutions

Apply parameter expansion flags to string or array literal in zsh

I think you are looking for :- parameter substitution:

$ restofarglist='abc,def'
$ echo ${(s/,/)${:-arg1,arg2,$restofarglist}}
arg1 arg2 abc def

From man zsh:

${name:-word}
              If name is set, or in the second form is non-null, then substitute its value;
              otherwise substitute word.  In the second form name may be omitted, in  which
              case word is always substituted.

Actually you can make this example a little bit shorter:

$ echo ${${:-arg1,arg2,$restofarglist}//,/ }
arg1 arg2 abc def

Zsh Expansion Syntax

Yes, your interpretation is correct (from skimming your long question).

Parameter expansion flags apply to parameter expansions. When you want it applied to any arbitrary string instead, you need to either store that string in a variable as in:

var=%1N
filename=${(%)var}

Or (as a hack) you can use the ${var:-string} parameter expansion and leave the var part empty: ${(%):-%1N}. That's a common trick(see ^{1
2
3
4
5
6
7
8
9
10
11
12
13} here for instance), though that makes for pretty illegible code. Alternatively, you could use the ${param+string} syntax and use a parameter like $- or $0 or $# that is always set (${(%)-+%1N}). That's neither shorter nor more legible though.

Here, you can also use print -P %1N

Best Answer

Related Solutions

Apply parameter expansion flags to string or array literal in zsh

Zsh Expansion Syntax

Related Question