O comportamento de expansão do prompt do Zsh é definido em man zshmisc
. Em relação à configuração de valores personalizados para o tamanho do prompt, ele diz:
%<string<
%>string>
%[xstring]
Specifies truncation behaviour for the remainder of the prompt
string. The third, deprecated, form is equivalent to
'%xstringx', i.e. x may be '<' or '>'. The string will be dis‐
played in place of the truncated portion of any string; note
this does not undergo prompt expansion.
The numeric argument, which in the third form may appear immedi‐
ately after the '[', specifies the maximum permitted length of
the various strings that can be displayed in the prompt. In the
first two forms, this numeric argument may be negative, in which
case the truncation length is determined by subtracting the
absolute value of the numeric argument from the number of char‐
acter positions remaining on the current prompt line. If this
results in a zero or negative length, a length of 1 is used. In
other words, a negative argument arranges that after truncation
at least n characters remain before the right margin (left mar‐
gin for RPROMPT).
The forms with '<' truncate at the left of the string, and the
forms with '>' truncate at the right of the string. For exam‐
ple, if the current directory is '/home/pike', the prompt
'%8<..<%/' will expand to '..e/pike'. In this string, the ter‐
minating character ('<', '>' or ']'), or in fact any character,
may be quoted by a preceding '\'; note when using print -P, how‐
ever, that this must be doubled as the string is also subject to
standard print processing, in addition to any backslashes
removed by a double quoted string: the worst case is therefore
'print -P "%<\\<<..."'.
If the string is longer than the specified truncation length, it
will appear in full, completely replacing the truncated string.
The part of the prompt string to be truncated runs to the end of
the string, or to the end of the next enclosing group of the
'%(' construct, or to the next truncation encountered at the
same grouping level (i.e. truncations inside a '%(' are sepa‐
rate), which ever comes first. In particular, a truncation with
argument zero (e.g., '%<<') marks the end of the range of the
string to be truncated while turning off truncation from there
on. For example, the prompt '%10<...<%~%<<%# ' will print a
truncated representation of the current directory, followed by a
'%' or '#', followed by a space. Without the '%<<', those two
characters would be included in the string to be truncated.
Note that '%-0<<' is not equivalent to '%<<' but specifies that
the prompt is truncated at the right margin.
Truncation applies only within each individual line of the
prompt, as delimited by embedded newlines (if any). If the
total length of any line of the prompt after truncation is
greater than the terminal width, or if the part to be truncated
contains embedded newlines, truncation behavior is undefined and
may change in a future version of the shell. Use
'%-n(l.true-text.false-text)' to remove parts of the prompt when
the available space is less than n.
A partir disso, você pode inferir
-
PROMPT="%/ "
lhe dará um diretório de trabalho
-
PROMPT='%10<..<%/ '
lhe dará um diretório de trabalho - se a cadeia do diretório de trabalho tiver mais de 10 caracteres, ela será truncada na borda esquerda e, quando ocorrer o truncamento, o padrão ..
será exibido (para indicar o valor aparado)
A largura do terminal pode ser obtida com $COLUMNS
, portanto, se você quiser um prompt restrito a 25% da largura do terminal, substitua o 10
por uma variável:
width=$(($COLUMNS / 4))
ou seja,
PROMPT="%${width}<..<%/ %% "