Awk One Liners Explained Pdf 40

My sed learning process was identical to Awk learning process. First, I went through Bruce Barnett's sed tutorial; then I created a sed cheat sheet; and then spent a couple of days going through sed one-liners file. I prepared a couple of test files with a bunch of random text lines and typed each one-liner in the command prompt and tried to decipher how it works. I couldn't figure out only one of the one-liners in the file, so I ended up asking for help in comp.unix.shell.

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This one-liner combines one-liners #5, #6 and #1. Lines matching /regex/ get a newline appended before them and printed (x;p;x from #5). Then they are followed by another newline from the 'G' command (one-liner #6 or #1).

One-liners get trickier and trickier. This one-liner is actually two separate one-liners. The first sed one-liner uses a new command called '='. This command operates directly on the output stream and prints the current line number. There is no way to capture the current line number to pattern space. That's why the second one-liner gets called. The output of first one-liner gets piped to the input of second. The second one-liner uses another new command 'N'. The 'N' command appends a newline and the next line to current pattern space. Then the famous 's///' command gets executed which replaces the newline character just appended with a tab. After these operations the line gets printed out.

This one-liner is also actually two one-liners. The first one liner numbers the lines, just like #8. The second one-liner uses the 'N' command to join the line containing the line number with the actual line. Then it uses two substitute commands to right align the number. The first 's' command 's/^/ /' appends 5 white-spaces to the beginning of line. The second 's' command 's/ *(.6,)\n/\1 /' captures at least six symbols up to a newline and replaces the capture and newline with the back-reference '\1' and two more whitespace to separate line number from the contents of line.

This one-liner is again two one-liners. The output of the first one-liner gets piped to the input of second. The first one-liner filters out lines with at least one character in them. The regular expression '/./' says: match lines with at least one char in them. When the empty lines (containing just a newline) get sent to the pattern space, the newline character gets removed, so the empty lines do not get matched. The second one-liner does the same one-liner #8 did, except that only numbered lines get joined and printed out. Command '/./N' makes sure that empty lines are left as-is.

The exit status of an executed command is the value returned by thewaitpid system call or equivalent function. Exit statuses fall between 0 and 255, though, as explained below, the shell mayuse values above 125 specially. Exit statuses from shell builtins andcompound commands are also limited to this range. Under certaincircumstances, the shell will use special values to indicate specificfailure modes.

The shell allows control of the various characters used by thehistory expansion mechanism with the histchars variable,as explained above (see Bash Variables). The shell usesthe history comment character to mark history timestamps whenwriting the history file.

Bash implements essentially the same grammar, parameter andvariable expansion, redirection, and quoting as the Bourne Shell. Bash uses the POSIX standard as the specification ofhow these features are to be implemented. There are somedifferences between the traditional Bourne shell and Bash; thissection quickly details the differences of significance. Anumber of these differences are explained in greater depth inprevious sections.This section uses the version of sh included in SVR4.2 (thelast version of the historical Bourne shell) as the baseline reference.

Algebraic laws for regular expressions can be obtained using a method by Gischer which is best explained along an example: In order to check whether (X+Y)* and (X* Y*)* denote the same regular language, for all regular expressions X, Y, it is necessary and sufficient to check whether the particular regular expressions (a+b)* and (a* b*)* denote the same language over the alphabet Î=a,b. More generally, an equation E=F between regular-expression terms with variables holds if, and only if, its instantiation with different variables replaced by different symbol constants holds.[25][26]

The origin of hexaploid bread wheat has long been the subject of intense scrutiny. Archeological and genetic evidence suggests that diploid and tetraploid wheats were first cultivated 10,000 years ago in the Fertile Crescent (Fig. 1a)5,6. The expansion of tetraploid wheat cultivation northeast into Caspian Iran and towards the Caucasus region resulted in sympatry with Ae. tauschii and the emergence of hexaploid bread wheat6. Ae tauschii displays a high level of genetic differentiation among local populations, and genetic marker analysis suggests that the wheat D subgenome donor was recruited from an L2 population of Ae. tauschii in the southwestern coastal area of the Caspian Sea8. However, not all the diversity within the wheat D subgenome can be explained by a single hybridization event6,44,45. Our population genomic analysis revealed the existence of a third lineage of Ae. tauschii, L3, which also contributed to the extant wheat genome. For example, a glutenin allele required for superior dough quality was recently found to be of L3 origin46. L3 accessions are restricted to present-day Georgia and may represent a relict population from a glacial refugium as observed in Arabidopsis47. We observed genomic signatures specific to L2 and L3 in hexaploid wheat supporting the multiple hybridization hypothesis (Fig. 1g).

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