Bash select valid rows from file with awk

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awk - f command in unix

I have a large data set with some invalid rows. I want to copy to another file only rows which start with valid date (regex digits).

Basically check if awk $1 is digit ([0-9]), if yes, write whole row ($0) to output file, if no skip this row, go to next row.

How I imagine it like (both versions give syntax error):

awk '{if ($1 =~ [0-9]) print $0 }' >> output.txt
awk '$1 =~ [0-9] {print $0}' filename.txt

while this does print the first field, I have no idea how to proceed.

awk '{ print $1 }' filename.txt
19780101
19780102
19780103
a
19780104
19780105
19780106
...

Full data set:

19780101    1   1   1   1   1
19780102    2   2   2   2   2
19780103    3   3   3   3   3
a   a   a   a   a   a
19780104    4   4   4   4   4
19780105    5   5   5   5   5
19780106    6   6   6   6   6
19780107    7   7   7   7   7
19780108    8   8   8   8   8
19780109    9   9   9   9   9
19780110    10  10  10  10  10
19780111    11  11  11  11  11
19780112    12  12  12  12  12
19780113    13  13  13  13  13
19780114    14  14  14  14  14
19780115    15  15  15  15  15
19780116    16  16  16  16  16
a   a   a   a   a   a
19780117    17  17  17  17  17
19780118    18  18  18  18  18
19780119    19  19  19  19  19
19780120    20  20  20  20  20

The data set can be reproduced with R

library(dplyr)
library(DataCombine)
N  <- 20
df = as.data.frame(matrix(seq(N),nrow=N,ncol=5))
df$date = format(seq.Date(as.Date('1978-01-01'), by = 'day', len = N), "%Y%m%d")
df <- df %>% select(date, everything())

df <- InsertRow(df, NewRow = rep("a", 6), RowNum = 4)
df <- InsertRow(df, NewRow = rep("a", 6), RowNum = 18)
write.table(df,"filename.txt", quote = FALSE, sep="\t",row.names=FALSE)

Questions about reading first N rows don't address my need, because my invalid rows could be anywhere. This solution doesn't work for some reason.

Since you have a large data set and such a simple requirement, you could just use grep for this as it'd be faster than awk:

grep '^[0-9]' file

Using AWK to select rows with specific value in specific column , The file that you run the script on has DOS line-endings. It may be that it was created on a Windows machine. Use dos2unix to convert it to a Unix text file. An easy task in R, but because of the size of the file and R objects being memory bound, reading the whole file in was too much for my student’s computer to handle. She sent me the below sample file and how she wanted to filter it. I chose AWK because it is designed for this type of task. It parses data line-by-line and doesn’t need to read

Based on your data, you can check if first column has 8 digits to be representing a date in YYYYMMDD format using this command:

awk '$1 ~ /^[0-9]{8}$/' file > output

awk to select rows based on condition on column, i mean i want to select rows only when 8th character of the line is 0. awk '{​chaine=substr($0,8,1);if (chaine==0) print $0}' file parameter LOG:015608::​ERR:2471:map_dgdrec:Invalid parameter LOG:015608::ERR:2487:map_nnmrec​:Invalid  20 awk examples. Many utility tools exist in the Linux operating system to search and generate a report from text data or file. The user can easily perform many types of searching, replacing and report generating tasks by using awk, grep and sed commands. awk is not just a command.

You can also try this..

sed '/^[0-9]/!d' inputfile > outputfile

How To Use awk In Bash Scripting, For e.g. display all lines from Apache log file if HTTP error code is 500 (9th This code calls awk to print selected fields from the ldd output:  The awk command was named using the initials of the three people who wrote the original version in 1977: Alfred Aho, Peter Weinberger, and Brian Kernighan. These three men were from the legendary AT&T Bell Laboratories Unix pantheon.

You can just go with this:

awk '/^[0-9]+/' file.txt  >> output.txt

By default awk works with lines, so you tell him (I am assuming he is a boy) to select the lines that starts (^) with at least one digit ([0-9]+), and to print them, redirecting in output.txt.

Hope helps.

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Awk - A Tutorial and Introduction - by Bruce Barnett, This section discusses AWK, another cornerstone of UNIX shell programming. AWK is an excellent tool for processing these rows and columns, and is easier adds one line before and one line after the input file. AWK supports extended regular expressions, so the following are examples of valid tests:. I have 2 files, file01= 7 columns, row unknown (but few) file02= 7 columns, row unknown (but many) now I want to create an output with the first field that is shared in both of them and then subtract the results from the rest of the fields and print there e.g. file 01 James|0|50|25|10|50|30

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Using AWK to Filter Rows · Tim Dennis, After attending a bash class I taught for Software Carpentry, a student contacted me We can also use AWK to select and print parts of the file. In the file marks.txt, the third column contains the subject name and the fourth column contains the marks obtained in a particular subject. Let us print these two columns using AWK print command. In the above example, $3 and $4 represent the third and the fourth fields respectively from the input record. Printing All Lines

Comments
  • You don't need to write {print} since that's the default action and you don't need + in the regexp since any string of 1 or more digits includes a string of 1 digit and so matches without it.