02-27-2020
Yes, $2 (USER=MICKEY) is split at the equals sign into array T , and then rebuilt with the lower case username in T[2].
The !a[$0]++ is a trick (independent of $2): a[$0] evaluates to FALSE if it equals zero or doesn't exist or is created on first reference, so its negation is TRUE and triggers the default action: print. Then it is "post incremented" and will never (OK, not until reaching / crossing MAX_INT) trigger again. So any further occurrences of $0 are suppressed.
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paste(1) General Commands Manual paste(1)
Name
paste - merge file data
Syntax
paste file1 file2...
paste -dlist file1 file2...
paste -s [-dlist] file1 file2...
Description
In the first two forms, concatenates corresponding lines of the given input files file1, file2, etc. It treats each file as a column or
columns of a table and pastes them together horizontally (parallel merging).
In the last form, the command combines subsequent lines of the input file (serial merging).
In all cases, lines are glued together with the tab character, or with characters from an optionally specified list. Output is to the
standard output, so it can be used as the start of a pipe, or as a filter, if - is used in place of a file name.
Options
- Used in place of any file name, to read a line from the standard input. (There is no prompting).
-dlist Replaces characters of all but last file with nontabs characters (default tab). One or more characters immediately following -d
replace the default tab as the line concatenation character. The list is used circularly, i. e. when exhausted, it is reused. In
parallel merging (i. e. no -s option), the lines from the last file are always terminated with a new-line character, not from the
list. The list may contain the special escape sequences:
(new-line), (tab), \ (backslash), and (empty string, not a null
character). Quoting may be necessary, if characters have special meaning to the shell (for example, to get one backslash, use
-d"\\" ).
Without this option, the new-line characters of each but the last file (or last line in case of the -s option) are replaced by a
tab character. This option allows replacing the tab character by one or more alternate characters (see below).
-s Merges subsequent lines rather than one from each input file. Use tab for concatenation, unless a list is specified with -d
option. Regardless of the list, the very last character of the file is forced to be a new-line.
Examples
ls | paste -d" " -
list directory in one column
ls | paste - - - -
list directory in four columns
paste -s -d"
" file
combine pairs of lines into lines
Diagnostics
line too long
Output lines are restricted to 511 characters.
too many files
Except for -s option, no more than 12 input files may be specified.
See Also
cut(1), grep(1), pr(1)
paste(1)