screen has a number of string escapes it uses for building various
strings. Most are replaced by text when the string is built, but the
=, <, and > escapes control a string's formatting by either
adding spaces or deleting characters.
These escapes are mostly used in formatting hardstatus/caption lines. The examples on this page all demonstrate uses of the truncation/padding escapes in the caption line for a 60-column screen window. For every example string, two status lines are shown: one for a screen session with three windows (so the window list is shorter than the caption length), and one for a screen session with 11 windows (so the window list is longer than the caption length).
The base from which all the examples vary is the caption string “[%H]%-w(%n-%t)%+w[%d/%m %c]”, which displays the hostname, a list of windows with the current window in parentheses, and the date and time.
caption always "[%H]%-w(%n-%t)%+w[%d/%m %c]" [mithrandir]0 zsh (1-zsh) 2 zsh[09/12 12:00] [mithrandir]0 zsh 1 zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 zs
If the = escape is specified with no arguments, e.g. %=, screen
will replace it with enough spaces to make the status string exactly as
wide as the display. If more than one such escape is present in the
string, screen will split the spaces evenly between all the escapes.
caption always "[%H]%=%-w(%n-%t)%+w[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) 2 zsh[09/12 12:00] [mithrandir] 0 zsh 1 zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 z
caption always "[%H]%=%-w(%n-%t)%+w%=[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithrandir] 0 zsh 1 zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 z
If a number is given as a parameter to the = escape, screen uses that
number as a percentage of the display width and either adds spaces at the
point or removes characters to the left of the point in order to place
that point at the specified location on the screen.
caption always "[%H]%10=%-w(%n-%t)%+w%50=[%d/%m %c]" [mithr0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithr0 zsh 1 zsh 2 zsh 3 z[09/12 12:00]
Note that you can do silly things like putting a smaller size later in the
string than a larger size, like %H%50=%w%20= and screen will happily
pad (or truncate) the string to the first size, add any additional
escapes, and then truncate down to the smaller size.
caption always "[%H]%50=%-w(%n-%t)%+w%20=[%d/%m %c]" [mithrandir][09/12 12:00] [mithrandir][09/12 12:00]
If the numeric parameter starts with a zero, screen considers it to be an
absolute position, rather than a percentage. Thus, while %5= refers
to a point 5% from the left of the screen, %05= refers to the fifth
character in the string.
caption always "[%H]%020=%-w(%n-%t)%+w%050=[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) 2 zsh [09/12 12: [mithrandir] 0 zsh 1 zsh 2 zsh 3 zsh 4 [09/12 12:
The numeric parameter may be preceeded by either a plus sign or a minus sign. If a minus sign is used, screen calculates the distance from the right side of the screen, not the left. If a plus sign is used, screen calculates the distance from the last truncation/padding point. Note that percentages are calculated based on the remaining space, not the total space.
Note the some versions of screen (including at least screen 4.00.03) do not calculate right-aligned numbers as percentages; they always consider them to be absolute values, even without a leading zero.
caption always "[%H]%25=%-w(%n-%t)%+w%-25=[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) 2 zs[09/12 12:00] [mithrandir] 0 zsh 1 zsh 2 zsh [09/12 12:00]
caption always "[%H]%50=%-w(%n-%t)%+w%+50=[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) [09/12 12:00] [mithrandir] 0 zsh 1 zsh 2[09/12 12:00]
If the numeric parameter is followed by an L, screen will only add
padding at that point. If truncation would otherwise be needed, screen
will do nothing.
caption always "[%H]%0L=%-w(%n-%t)%+w%60L=[%d/%m %c]" [mithrandir]0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithrandir]0 zsh 1 zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 zs
The < escape takes exactly the same set of arguments as the =
escape, but it's the opposite of using the L flag with the =
escape: it will only truncate strings; if padding would otherwise be
needed, the < escape will do nothing.
In other words, you have three truncation/padding choices: %= will try
to place the escape at exactly the specified point; %L= will place the
escape at the specified point only if it can do it by adding spaces to the
string; and %< will place the escape at the specified point only if it
can do it by truncating the string.
caption always "[%H]%0<%-w(%n-%t)%+w%50<[%d/%m %c]" 0 zsh (1-zsh) 2 zsh[09/12 12:00] 0 zsh 1 zsh 2 zsh 3 zsh 4 [09/12 12:00]
The > escape requires a numeric parameter, e.g. %20>. When screen
must truncate a string that contains a > escape, it will truncate the
string from both ends as necessary to place the escape a percentage of the
way into the truncation space, where the percentage is the number
specified as a parameter. The “truncation space” extends from the first
truncation/padding point on the left of the > escape to the first
truncation/padding point on the right of the > escape. If there's no
such point on the left, the beginning of the string is used. If there's
no such point on the right, the escape is ignored. (i.e. the right edge
of the screen is not considered a proper truncation point.)
caption always "[%H]%-w%45>(%n-%t)%+w[%d/%m %c]" [mithrandir]0 zsh (1-zsh) 2 zsh[09/12 12:00] [mithrandir]0 zsh 1 zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 zs
caption always "[%H]%-w%45>(%n-%t)%+w[%d/%m %c]%-0=" [mithrandir]0 zsh (1-zsh) 2 zsh[09/12 12:00] zsh 2 zsh 3 zsh 4 zsh (5-zsh) 6 zsh 7 zsh 8 zsh 9 z
It can often be useful to narrow the boundaries of the > escape's
truncation space, to avoid problems like the last example's removal of the
hostname. An easy way to do this is to add a %L= at the desired
boundary.
caption always "[%H]%L=%-w%45>(%n-%t)%+w%-13=[%d/%m %c]" [mithrandir]0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithrandir] 3 zsh 4 zsh (5-zsh) 6 zsh 7 zs[09/12 12:00]
If the numeric parameter is followed by a L, screen will add ellipses
to mark where truncation has taken place.
caption always "[%H]%L=%-w%45L>(%n-%t)%+w%-13=[%d/%m %c]" [mithrandir]0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithrandir]...zsh 4 zsh (5-zsh) 6 zsh 7...[09/12 12:00] [mithrandir]0 zsh 1 zsh (2-zsh) 3 zsh 4 ...[09/12 12:00]
The > escape only kicks in if a string is truncated; if padding is
needed, not only does it not do anything, it appears to interfere with
padding insertions (at least as of screen 4.00.03). One general-purpose
workaround to this problem is to have adjacent truncation/padding points
at the boundaries of the > escape's truncation space.
caption always "[%H]%L=%=%-w%45L>(%n-%t)%+w%=%-13=[%d/%m %c]" [mithrandir] 0 zsh (1-zsh) 2 zsh [09/12 12:00] [mithrandir]...zsh 4 zsh (5-zsh) 6 zsh 7...[09/12 12:00] [mithrandir] 0 zsh 1 zsh (2-zsh) 3 zsh 4...[09/12 12:00]