Linux data often comes in streams of bytes or lines of text. The October 2004 “Power Tools” column presented some ways to edit data byte-by-byte. This month, let’s look at tools and techniques for slicing and dicing data in words and lines, including grouping arguments with xargs and fmt, other uses of fmt and fold, joining lines with join, and turning lines into tables with column and printf.
There’s a lot to cover this month, so let’s dig in!
Groups of Arguments
Early Unix systems had limited amounts of memory, and so it was easy to “run out of room” on the command-line. For example, in a directory with hundreds of files, a command like grep"some words"*, where the * wildcard expands into all of the names in the directory, often gave an error like Arguments too long. But even on modern systems without similar limitations, it is still very useful to understand the problem and to be able to work around it.
Let’s start with a quick review of how a shell executes a program, passes command-line arguments to it, and handles its standard I/O.
When a shell executes a command line like this one…
$ grep "some words" * > /tmp/grepout
… the shell first parses the command line. The first word is the name of the program to execute; the shell finds the executable program at (in this case) /bin/grep. The quotes around some words tell the shell not…
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