Change width of man command ouput

As pointed out in other answers, setting and exporting MANWIDTH properly is the way to go.

I would avoid hardcoding it, or else it will overflow / have ugly linebreaks when your terminal emulator window is more narrow than that value:

NAME
       grep, egrep, fgrep - print lines that match
 patterns

SYNOPSIS
       grep [OPTION...] PATTERNS [FILE...]
       grep [OPTION...] -e PATTERNS ... [FILE...]
       grep [OPTION...] -f PATTERN_FILE ... [FILE.
..]

DESCRIPTION
       grep  searches  for  PATTERNS  in  each  FI
LE.  PATTERNS is one or more
       patterns separated by newline characters, a
nd  grep  prints  each  line
       that  matches a pattern.  Typically PATTERN
S should be quoted when grep
       is used in a shell command.

Here's what I use, in a handy alias:

alias man='MANWIDTH=$((COLUMNS > 80 ? 80 : COLUMNS)) man'

This sets MANWIDTH to 80 if the terminal window is wider than that, and to COLUMNS (the current width of the terminal window) if it is more narrow.

Result in a wide window:

NAME
       grep, egrep, fgrep - print lines that match patterns

SYNOPSIS
       grep [OPTION...] PATTERNS [FILE...]
       grep [OPTION...] -e PATTERNS ... [FILE...]
       grep [OPTION...] -f PATTERN_FILE ... [FILE...]

DESCRIPTION
       grep  searches  for  PATTERNS  in  each  FILE.  PATTERNS is one or more
       patterns separated by newline characters, and  grep  prints  each  line
       that  matches a pattern.  Typically PATTERNS should be quoted when grep
       is used in a shell command.

Result in a narrow window:

NAME
       grep,  egrep, fgrep - print lines that
       match patterns

SYNOPSIS
       grep [OPTION...] PATTERNS [FILE...]
       grep  [OPTION...]  -e   PATTERNS   ...
       [FILE...]
       grep  [OPTION...]  -f PATTERN_FILE ...
       [FILE...]

DESCRIPTION
       grep searches  for  PATTERNS  in  each
       FILE.    PATTERNS   is   one  or  more
       patterns    separated    by    newline
       characters,  and grep prints each line
       that  matches  a  pattern.   Typically
       PATTERNS should be quoted when grep is
       used in a shell command.

You need to set this as an environment variable.

MANWIDTH=80 man man

works here, and provides the manpage for man in 80 column glory.

If you want this in .bashrc the correct line entry is

export MANWIDTH=80

Note lack of spaces around = sign. You may or may not need export.

That's an environment variable.

Try:

MANWIDTH=80
export MANWIDTH
man bash

If you want that set permanently then you can add those first two lines to your shell session startup scripts or similar.