Bash 101 - to (do) ; or not to (do) ; ? Post: 303022252

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Top Forums Shell Programming and Scripting Bash 101 - to (do) ; or not to (do) ; ? Post 303022252 by bakunin on Tuesday 28th of August 2018 05:18:15 PM

08-28-2018

Registered User

Quote:

Originally Posted by annacreek

Code:

while [ $i -lt 4 ] do xterm & i=$[$i+1] done

I don't know from which "manual" you got that, but there are more errors then correct words in it. Shame on whoever wrote this drivel. The correct form would be:

Code:

while [ $i -lt 4 ] ; do xterm & ; (( i = i+1 )) ; done

or, in a more readable way:

Code:

while [ $i -lt 4 ] ; do
     xterm &
     (( i = i+1 ))
done

Note that [ is actually a real command: it is a different way to invoke /bin/test. Written in "long form" where the command is more easily recognisable it would be:

Code:

while /bin/test $i -lt 4 ; do
     xterm &
     (( i = i+1 ))
done

The command

Code:

/bin/test $i -lt 4

will return 0 (logical TRUE) if the variable i is lower than 4 and 1 (logically FALSE) otherwise. The while-loop is repeated as long as the control-command (in this case /bin/test) returns 0 and stops if it returns 1. The following will read a complete file:

Code:

while read LINE ; do
     echo "== $LINE =="
done < /some/file

because the read-command returns 0 as long as it can read a line but returns 1 when it hits end-of-file.

I hope this helps.

bakunin

bakunin

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resize

resize(1X)																resize(1X)

NAME

       resize - set TERMCAP and terminal settings to current xterm window size

SYNOPSIS

       resize [-u] [-c] [-s[row col]]

OPTIONS

       The following options may be used with resize: This option indicates that Bourne shell commands should be generated even if the user's cur-
       rent shell is not /bin/sh.  This option indicates that C shell commands should be generated  even  if  the  user's  current  shell  is  not
       /bin/csh.  This option indicates that Sun console escape sequences will be used instead of the special xterm escape code.  If rows and col-
       umns are given, resize will ask the xterm to resize itself.  However, the window manager may choose to disallow the change.

DESCRIPTION

       The resize command prints a shell command for setting the TERM and TERMCAP environment variables to indicate the current size of xterm win-
       dow  from  which  the command is run.  For this output to take effect, resize must either be evaluated as part of the command line (usually
       done with a shell alias or function) or else redirected to a file which can then be read in.  From the C shell (usually known as /bin/csh),
       the following alias could be defined in the user's
	       %  alias rs 'set noglob; eval `resize`'

       After resizing the window, the user would type: %  rs

       Users  of versions of the Bourne shell (usually known as /bin/sh) that do not have command functions will need to send the output to a tem-
       porary file and the read it back in with the "." command:
	       $  resize > /tmp/out
	       $  . /tmp/out

FILES

       for the base termcap entry to modify.  user's alias for the command.

BUGS

       The -u or -c must appear to the left of -s if both are specified.

SEE ALSO

       csh(1), tset(1), xterm(1X)

AUTHORS

       Mark Vandevoorde (MIT-Athena), Edward Moy (Berkeley)
       Copyright (c) 1984, 1985 by X Consortium

       See X(1X) for a complete copyright notice.

																	resize(1X)

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resize