One regularly sees here situations where some poor punter is flamed fro what
the flamer calls useless use of cat e.g. where someone might have said
cat file|some_program
rather than
some_program < file
However, today I came across a necessary, but apparently useless use of cat.
I had a file with a list of images and some characteristics of those images,
including their format. I wanted to extract all JPEGs and TIFFs so I
naturally tried
niall at bagend:/mnt/images :1>egrep "JPEG|TIFF" imagelist.txt
Binary file imagelist.txt matches
niall at bagend:/mnt/images :2>egrep "JPEG|TIFF" < imagelist.txt
Binary file (standard input) matches
niall at bagend:/mnt/images :3>cat imagelist.txt | egrep "JPEG|TIFF"
.
.
.
lots of output
.
.
.
Now a quick perusal of the grep (egrep being of course just grep wearing
fancy clothes) manual taught me that -a was my friend, but I'm still very
puzzled by the difference between 2 and 3, when in each case egrep surely
sees only that it has a non-TTY as its stdin.
Regards,
Niall
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