I see the following output of gcc preprocessing. I don't find the documentation of the output format. Could anybody let me know what it is? Thanks.
$ cat a.h
#include "b.h"
$ cat b.h
#define X Y
$ gcc -E -dD - <<< '#include "a.h"'
...
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "<stdin>" 2
# 1 "./a.h" 1
# 1 "./b.h" 1
#define X Y
# 2 "./a.h" 2
# 2 "<stdin>" 2
When I try the following, I see more numbers, which are different from the above. I am not sure about what they mean either.
$ gcc -E -dD - <<< '#include <sys/socket.h>'
...
# 19 "/usr/include/x86_64-linux-gnu/asm/posix_types_64.h" 2 3 4
# 8 "/usr/include/x86_64-linux-gnu/asm/posix_types.h" 2 3 4
# 37 "/usr/include/linux/posix_types.h" 2 3 4
# 6 "/usr/include/asm-generic/socket.h" 2 3 4
# 1 "/usr/include/x86_64-linux-gnu/asm/sockios.h" 1 3 4
# 1 "/usr/include/asm-generic/sockios.h" 1 3 4
...
Unusual lines are linemarkers, which specify linenumber and filename. Numbers after the filename are special flags.
These are explained in GCC Preprocessor online documentation:
Source file name and line number information is conveyed by lines of
the form
# linenum filename flags
These are called linemarkers. They are inserted as needed into the
output (but never within a string or character constant). They mean
that the following line originated in file filename at line linenum.
filename will never contain any non-printing characters; they are
replaced with octal escape sequences.
After the file name comes zero or more flags, which are ‘1’, ‘2’, ‘3’,
or ‘4’. If there are multiple flags, spaces separate them. Here is
what the flags mean:
‘1’ This indicates the start of a new file.
‘2’ This indicates returning to a file (after having included another file).
‘3’ This indicates that the following text comes from a system header file, so certain warnings should be suppressed.
‘4’ This indicates that the following text should be treated as being wrapped in an implicit extern "C" block.
Related
suppose I have file containing numbers like:
1 4 7
2 5 8
and I want to add 1 to all these numbers, making the output like:
2 5 8
3 6 9
is there a simple one-line command (e.g. awk) to realize this?
try following once.
awk '{for(i=1;i<=NF;i++){$i=$i+1}} 1' Input_file
EDIT: As per OP's request without loop, here is a solution(written as per shown sample only).
With hardcoding of number of fields.
awk -v RS='[ \n]' '{ORS=NR%3==0?"\n":" ";print $0+1}' Input_file
OR
Without hardcoding number of fields.
awk -v RS='[ \n]' -v col=$(awk 'FNR==1{print NF}' Input_file) '{ORS=NR%col==0?"\n":" ";print $0+1}' Input_file
Explanation: So in EDIT section 1st solution I have hardcoded the number of fields by mentioning 3 there, in OR solution of EDIT, I am creating a variable named col which will read the very first line of Input_file to get the number of fields. Then it will not read all the Input_file, Now coming onto the code I have set Record separator as space or new line to it will add them without using a loop and it will add space each time after incrementing 1 in their values. It will print new line only when number of lines are completely divided by value of col(which is why we have taken number of fields in -v col section).
In native bash (no awk or other external tool needed):
#!/usr/bin/env bash
while read -r -a nums; do # read a line into an array, splitting on spaces
out=( ) # initialize an empty output array for that line
for num in "${nums[#]}"; do # iterate over the input array...
out+=( "$(( num + 1 ))" ) # ...and add n+1 to the output array.
done
printf '%s\n' "${out[*]}" # then print that output array with a newline following
done <in.txt >out.txt # with input from in.txt and output to out.txt
You can do this using gnu awk:
awk -v RS="[[:space:]]+" '{$0++; ORS=RT} 1' file
2 5 8
3 6 9
If you don't mind Perl:
perl -pe 's/(\d+)/$1+1/eg' file
Substitute any number composed of multiple digits (\d+) with that number ($1) plus 1. /e means to execute the replacement calculation, and /g means globally throughout the file.
As mentioned in the comments, the above only works for positive integers - per the OP's original sample file. If you wanted it to work with negative numbers, decimals and still retain text and spacing, you could go for something like this:
perl -pe 's/([-]?[.0-9]+)/$1+1/eg' file
Input file
Some column headers # words
1 4 7 # a comment
2 5 cat dog # spacing and stray words
+5 0 # plus sign
-7 4 # minus sign
+1000.6 # positive decimal
-21.789 # negative decimal
Output
Some column headers # words
2 5 8 # a comment
3 6 cat dog # spacing and stray words
+6 1 # plus sign
-6 5 # minus sign
+1001.6 # positive decimal
-20.789 # negative decimal
For a file that contains entries similar to as follows:
foo 1 6 0
fam 5 11 3
wam 7 23 8
woo 2 8 4
kaz 6 4 9
faz 5 8 8
How would you replace the nth field of every mth line with the same element using bash or awk?
For example, if n = 1 and m = 3 and the element = wot, the output would be:
foo 1 6 0
fam 5 11 3
wot 7 23 8
woo 2 8 4
kaz 6 4 9
wot 5 8 8
I understand you can call / print every mth line using e.g.
awk 'NR%7==0' file
So far I have tried to keep this in memory but to no avail... I need to keep the rest of the file as well.
I would prefer answers using bash or awk, but sed solutions would also be helpful. I'm a beginner in all three. Please explain your solution.
awk -v m=3 -v n=1 -v el='wot' 'NR % m == 0 { $n = el } 1' file
Note, however, that the inter-field whitespace is not guaranteed to be preserved as-is, because awk splits a line into fields by any run of whitespace; as written, the output fields of modified lines will be separated by a single space.
If your input fields are consistently separated by 2 spaces, however, you can effectively preserve the input whitespace by adding -F' ' -v OFS=' ' to the awk invocation.
-v m=3 -v n=1 -v el='wot' defines Awk variables m, n, and el
NR % m == 0 is a pattern (condition) that evaluates to true for every m-th line.
{ $n = el } is the associated action that replaces the nth field of the input line with variable el, causing the line to be rebuilt, implicitly using OFS, the output-field separator, which defaults to a space.
1 is a common Awk shorthand for printing the (possibly modified) input line at hand.
Great little exercise. While I would probably lean toward an awk solution, in bash you can also rely on parameter expansion with substring replacement to replace the nth field of every mth line. Essentially, you can read every line, preserving whitespace, then check your line count, e.g. if c is your line counter and m your variable for mth line, you could use:
if (( $((c % m )) == 0)) ## test for mth line
If the line is a replacement line, you can read each word into an array after restoring default word-splitting and then use your array element index n-1 to provide the replacement (e.g. ${line/find/replace} with ${line/"${array[$((n-1))]}"/replace}).
If it isn't a replacement line, simply output the line unchanged. A short example could be similar to the following (to which you can add additional validations as required)
#!/bin/bash
[ -n "$1" -a -r "$1" ] || { ## filename given an readable
printf "error: insufficient or unreadable input.\n"
exit 1
}
n=${2:-1} ## variables with default n=1, m=3, e=wot
m=${3:-3}
e=${4:-wot}
c=1 ## line count
while IFS= read -r line; do
if (( $((c % m )) == 0)) ## test for mth line
then
IFS=$' \t\n'
a=( $line ) ## split into array
IFS=
echo "${line/"${a[$((n-1))]}"/$e}" ## nth replaced with e
else
echo "$line" ## otherwise just output line
fi
((c++)) ## advance counter
done <"$1"
Example Use/Output
n=1, m=3, e=wot
$ bash replmn.sh dat/repl.txt
foo 1 6 0
fam 5 11 3
wot 7 23 8
woo 2 8 4
kaz 6 4 9
wot 5 8 8
n=1, m=2, e=baz
$ bash replmn.sh dat/repl.txt 1 2 baz
foo 1 6 0
baz 5 11 3
wam 7 23 8
baz 2 8 4
kaz 6 4 9
baz 5 8 8
n=3, m=2, e=99
$ bash replmn.sh dat/repl.txt 3 2 99
foo 1 6 0
fam 5 99 3
wam 7 23 8
woo 2 99 4
kaz 6 4 9
faz 5 99 8
An awk solution is shorter (and avoids problems with duplicate occurrences of the replacement string in $line), but both would need similar validation of field existence, etc.. Learn from both and let me know if you have any questions.
I am trying to figure out how to write a bash script which uses the lines immediately before and after a line as a condition. I will give an example in a python-like pseudocode which makes sense to me.
Basically:
for line in FILE:
if line_minus_1 == line_plus_one:
line = line_minus_1
What would be the best way to do this?
So if I have an input file that reads:
3
1
1
1
2
2
1
2
1
1
1
2
2
1
2
my output would be:
3
1
1
1
2
2
2
2
1
1
1
2
2
2
2
Notice that it starts from the first line until the last line and respects changes made in earlier lines so if I have:
2
1
2
1
2
2
I would get:
2
2
2
2
2
2
and not:
2
1
1
1
2
2
$ awk 'minus2==$0{minus1=$0} NR>1{print minus1} {minus2=minus1; minus1=$0} END{print minus1}' file
3
1
1
1
2
2
2
2
1
1
1
2
2
2
2
How it works
minus2==$0{minus1=$0}
If the line from 2 lines ago is the same as the current line, then set the line from 1 line ago equal to the current line.
NR>1{print minus1}
If we are past the first line, then print the line from 1 line ago.
minus2=minus1; minus1=$0
Update the variables.
END{print minus1}
After we have finished reading the file, print the last line.
Multiple line version
For those who like their code spread over multiple lines:
awk '
minus2==$0{
minus1=$0
}
NR>1{
print minus1
}
{
minus2=minus1
minus1=$0
}
END{
print minus1
}
' file
Here is a (GNU) sed solution:
$ sed -r '1N;N;/^(.*)\n.*\n\1$/s/^(.*\n).*\n/\1\1/;P;D' infile
3
1
1
1
2
2
2
2
1
1
1
2
2
2
2
This works with a moving three line window. A bit more readable:
sed -r ' # -r for extended regular expressions: () instead of \(\)
1N # On first line, append second line to pattern space
N # On all lines, append third line to pattern space
/^(.*)\n.*\n\1$/s/^(.*\n).*\n/\1\1/ # See below
P # Print first line of pattern space
D # Delete first line of pattern space
' infile
N;P;D is the idiomatic way to get a moving two line window: append a line, print first line, delete first line of pattern space. To get a moving three line window, we read an additional line, but only once, namely when processing the first line (1N).
The complicated bit is checking if the first and third line of the pattern space are identical, and if they are, replacing the second line with the first line. To check if we have to make the substitution, we use the address
/^(.*)\n.*\n\1$/
The anchors ^ and $ are not really required as we'll always have exactly to newlines in the pattern space, but it makes it more clear that we want to match the complete pattern space. We put the first line into a capture group and see if it is repeated on the third line by using a backreference.
Then, if this is the case, we perform the substitution
s/^(.*\n).*\n/\1\1/
This captures the first line including the newline, matches the second line including the newline, and substitutes with twice the first line. P and D then print and remove the first line.
When reaching the end, the whole pattern space is printed so we're not swallowing any lines.
This also works with the second input example:
$ sed -r '1N;N;/^(.*)\n.*\n\1$/s/^(.*\n).*\n/\1\1/;P;D' infile2
2
2
2
2
2
2
To use with BSD sed (as found in OS X), you'd either have to use the -E instead of the -r option, or use no option, i.e., basic regular expressions and escape all parentheses (\(\)) in the capture groups. The newline matching should work, but I didn't test it. If in doubt, check this great answer lining out all the differences.
I'm having the following issue. I have an array of numbers:
text="\n1\t2\t3\t4\t5\n6\t7\t8\t9\t0"
And I'd like to delete the leading newline.
I've tried
sed 's/.//' <<< "$text"
cut -c 1- <<< "$text"
and some iterations. But the issue is that both of those delete the first character AFTER EVERY newline. Resulting in this:
text="\n\t2\t3\t4\t5\n\t7\t8\t9\t0"
This is not what I want and there doesn't seem to be an answer to this case.
Is there a way to tell either of those commands to treat newlines like characters and the entire string as one entity?
awk to the rescue!
awk 'NR>1'
of course you can do the same with tail -n +2 or sed 1d as well.
You can probably use the substitution modifier (see parameter expansion and ANSI C quoting in the Bash manual):
$ text=$'\n1\t2\t3\t4\t5\n6\t7\t8\t9\t0'
$ echo "$text"
1 2 3 4 5
6 7 8 9 0
$ echo "${text/$'\n'/}"
1 2 3 4 5
6 7 8 9 0
$
It replaces the first newline with nothing, as requested. However, note that it is not anchored to the first character:
$ alt="${text/$'\n'/}"
$ echo "${alt/$'\n'/}"
1 2 3 4 56 7 8 9 0
$
Using a caret ^ before the newline doesn't help — it just means there's no match.
As pointed out by rici in the comments, if you read the manual page I referenced, you can find how to anchor the pattern at the start with a # prefix:
$ echo "${text/#$'\n'/}"
1 2 3 4 5
6 7 8 9 0
$ echo "${alt/#$'\n'/}"
1 2 3 4 5
6 7 8 9 0
$
The notation bears no obvious resemblance to other regex systems; you just have to know it.
I'm getting an error when I try to use ## in macro this is what I try to make:
With this defines:
#define PORT 2
#define PIN 3
I want that preprocessor generates:
PM2.3=1
when I call a macro like this:
SetPort(PORT,PIN)
Then, I see that I can make the substitution PORT and PIN at the same time that concatenation, then I think I must to use 2 defines:
#define SetP2(PORT,PIN) PM##PORT.PIN = 1
#define SetPort(PORT,PIN) SetP2(PORT,PIN)
but I get an error on:
#define PIN 3 --> expected identifier before numeric constant
and a warning on:
SetPort(PORT,PIN) --> Syntax error
Any idea?
This works for me:
$ cat portpin.c
#define PORT 2
#define PIN 3
#define SetP2(prefix,prt) prefix ## prt
#define SetPort(prt,pn) SetP2(PM,prt).pn = 1
SetPort(PORT,PIN)
$ gcc -E portpin.c
# 1 "portpin.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "portpin.c"
PM2. 3 = 1
$
I don't know how important it is for there to be no space between the . and the 3, but the preprocessor seems to want to insert it.
UPDATE:
Actually I tried your original code, and it seems to produce the same result, so my answer above is probably not much use to you.
UPDATE 2:
It turns out the OP is expecting the pre-processor to generate PM2.no3=1 and not PM2.3=1. This can easily be done as follows:
$ cat portpin.c
#define PORT 2
#define PIN 3
#define SetP2(PORT,PIN) PM##PORT.no##PIN=1
#define SetPort(PORT,PIN) SetP2(PORT,PIN)
SetPort(PORT,PIN)
$ gcc -E portpin.c
# 1 "portpin.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "portpin.c"
PM2.no3=1
$