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Shell Programming and Scripting
Check for file existence using wildcards
Post 302363098 by Azhrei on Monday 19th of October 2009 11:27:44 AM
10-19-2009
Thanks for replying and including the solution you ended up using. 
Btw, that looks like C shell code due to the redirection syntax. You really don't want to use the C shell for any kind of production work; it's too buggy and idiosyncratic. Google for "101 reasons not to use the C shell".
A problem with both my code and yours is the assumption that the current directory is readable and thus ls(1) won't fail due to anything other than a wildcard not being replaced by the shell. In the real world this is a reasonable assumption, but truly defensive shell scripting would check for that with and additional if statement of [ -r . ]
Because both of our routines use ls(1) they pay a performance penalty for the fork() and exec() required to run ls(1). If all built-in commands could be used it would be much faster.
For example, using for i in *.[Ll][Aa][Ss]; do break; done would result in the wildcard being expanded but the loop breaking the very first time through. The value of i will either be a real filename (as the wildcard was expanded) or the string *.[Ll][Aa][Ss] and a simple [ -e "$i" ] will determine that. This solution requires no fork/exec and will be much faster.
But I'm betting that the performance is not a big issue anyway.
Btw, that looks like C shell code due to the redirection syntax. You really don't want to use the C shell for any kind of production work; it's too buggy and idiosyncratic. Google for "101 reasons not to use the C shell".
A problem with both my code and yours is the assumption that the current directory is readable and thus ls(1) won't fail due to anything other than a wildcard not being replaced by the shell. In the real world this is a reasonable assumption, but truly defensive shell scripting would check for that with and additional if statement of [ -r . ]
Because both of our routines use ls(1) they pay a performance penalty for the fork() and exec() required to run ls(1). If all built-in commands could be used it would be much faster.
For example, using for i in *.[Ll][Aa][Ss]; do break; done would result in the wildcard being expanded but the loop breaking the very first time through. The value of i will either be a real filename (as the wildcard was expanded) or the string *.[Ll][Aa][Ss] and a simple [ -e "$i" ] will determine that. This solution requires no fork/exec and will be much faster.
But I'm betting that the performance is not a big issue anyway.
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LEARN ABOUT MINIX
ppmtosixel
ppmtosixel(1) General Commands Manual ppmtosixel(1) NAME
ppmtosixel - convert a portable pixmap into DEC sixel format SYNOPSIS
ppmtosixel [-raw] [-margin] [ppmfile] DESCRIPTION
Reads a portable pixmap as input. Produces sixel commands (SIX) as output. The output is formatted for color printing, e.g. for a DEC LJ250 color inkjet printer. If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled. A printer control header and a color assignment table begin the SIX file. Image data is written in a compressed format by default. A printer control footer ends the image file. OPTIONS
-raw If specified, each pixel will be explicitly described in the image file. If -raw is not specified, output will default to com- pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands. A raw file is often an order of magni- tude larger than a compressed file and prints much slower. -margin If -margin is not specified, the image will be start at the left margin (of the window, paper, or whatever). If -margin is speci- fied, a 1.5 inch left margin will offset the image. PRINTING
Generally, sixel files must reach the printer unfiltered. Use the lpr -x option or cat filename > /dev/tty0?. BUGS
Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion. If the original PPM maxval was greater than 100, rescaling also reduces the image depth. While the actual RGB values from the ppm file are more or less retained, the color palette of the LJ250 may not match the colors on your screen. This seems to be a printer limitation. SEE ALSO
ppm(5) AUTHOR
Copyright (C) 1991 by Rick Vinci. 26 April 1991 ppmtosixel(1)