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Full Discussion: Unexpected result from awk
Top Forums UNIX for Beginners Questions & Answers Unexpected result from awk Post 303015419 by Don Cragun on Wednesday 4th of April 2018 03:23:10 PM
Old 04-04-2018
Quote:
Originally Posted by uniran
Hello,

Giving those commands:

Code:
cat > myfile 
1 
2 
3 
^D 
cat myfile | awk '{ s=s+$1 ; print s}'

The output is:

Code:
1
3
6

It seems like this command iterates each time on a different row so $1 is the first field of each row.. But what caused it to refer to each row ?.
What I mean is, how it knows that for the second iteration for example, $1 should be the first field of the second row rather then the first field of the first row again ?
Because:
  • that is the way awk is described to work,
  • there are no loops in your code to cause an input line in your file to be evaluated more than once,
  • if awk was designed to only process the 1st line in a file (instead of processing each line in a file), it wouldn't be able to process multi-million line input files,
  • et cetera.
What in the description of awk on your system made you think that awk should only process the first line in a file?
 

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cat(1)								   User Commands							    cat(1)

NAME
cat - concatenate and display files SYNOPSIS
cat [-nbsuvet] [file...] DESCRIPTION
The cat utility reads each file in sequence and writes it on the standard output. Thus: example% cat file prints file on your terminal, and: example% cat file1 file2 >file3 concatenates file1 and file2, and writes the results in file3. If no input file is given, cat reads from the standard input file. OPTIONS
The following options are supported: -n Precede each line output with its line number. -b Number the lines, as -n, but omit the line numbers from blank lines. -u The output is not buffered. (The default is buffered output.) -s cat is silent about non-existent files. -v Non-printing characters (with the exception of tabs, new-lines and form-feeds) are printed visibly. ASCII control characters (octal 000 - 037) are printed as ^n, where n is the corresponding ASCII character in the range octal 100 - 137 (@, A, B, C, . . ., X, Y, Z, [, , ], ^, and _); the DEL character (octal 0177) is printed ^?. Other non-printable characters are printed as M-x, where x is the ASCII character specified by the low-order seven bits. When used with the -v option, the following options may be used: -e A $ character will be printed at the end of each line (prior to the new-line). -t Tabs will be printed as ^I's and formfeeds to be printed as ^L's. The -e and -t options are ignored if the -v option is not specified. OPERANDS
The following operand is supported: file A path name of an input file. If no file is specified, the standard input is used. If file is `-', cat will read from the standard input at that point in the sequence. cat will not close and reopen standard input when it is referenced in this way, but will accept multiple occurrences of `-' as file. USAGE
See largefile(5) for the description of the behavior of cat when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes). EXAMPLES
Example 1: Concatenating a file The following command: example% cat myfile writes the contents of the file myfile to standard output. Example 2: Concatenating two files into one The following command: example% cat doc1 doc2 > doc.all concatenates the files doc1 and doc2 and writes the result to doc.all. Example 3: Concatenating two arbitrary pieces of input with a single invocation The command: example% cat start - middle - end > file when standard input is a terminal, gets two arbitrary pieces of input from the terminal with a single invocation of cat. Note, however, that if standard input is a regular file, this would be equivalent to the command: cat start - middle /dev/null end > file because the entire contents of the file would be consumed by cat the first time `-' was used as a file operand and an end-of-file condition would be detected immediately when `-' was referenced the second time. ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of cat: LANG, LC_ALL, LC_CTYPE, LC_MES- SAGES, and NLSPATH. EXIT STATUS
The following exit values are returned: 0 All input files were output successfully. >0 An error occurred. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |CSI |enabled | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
touch(1), attributes(5), environ(5), largefile(5), standards(5) NOTES
Redirecting the output of cat onto one of the files being read will cause the loss of the data originally in the file being read. For exam- ple, example% cat filename1 filename2 >filename1 causes the original data in filename1 to be lost. SunOS 5.10 1 Feb 1995 cat(1)
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