06-15-2013
Note that the cd utility is a shell built-in; so the results of a test like this could vary widely from shell to shell.
Most shells will need to set the variable PWD when they start. Some shells will remember some number of directories they have seen in calls to cd and if they have seen a target direcotry path before, they can change the value of PWD (a side effect of calling cd) by looking at an in memory cache of previously visited directories. When you renamed subfol3 to subfol4, the shell's cache didn't contain an entry for subfol4 and had to make at least one system call to determine if subfol4 was a real directory or a symbolic link to a directory.
When you renamed subfol4 back to subfol3, the shell's cache could have contained an entry for subfol3, so it may have assumed that its cache was still valid.
If you look at the truss output (instead of just looking at the getcwd line in the output) you might be able to glean what is going on under the covers. You haven't said whether either of the subfol3 or subfol4 directories had been visited before the output you showed. My guess would be that you had visited subfol3 before, to get the results you showed, but without a lot more details this is purely speculation.
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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)