Insert or transform (txt argument) one or more lines in a file specified
either by line number or a boolean function (match argument). Any file that
can be read with the readLines() function should be compatible.
Arguments
- file
chr, path to a file
- txt
chr or chr fun, either a single character string to insert into the file or a function that transforms a character string. If supplying a function, the first argument of the function must accept a single string and it must return a single string. The function will be applied independently to each line in the file that matches the match argument. Supports anonymous functions. See examples.
- match
num vector or lgl fun, either a numeric vector indicating line indices in the file or a function that returns a logical indicating lines to change. If supplying a function, the first argument of the function must accept a single string and it must return a logical vector. The function will be applied independently to each line in the file. Supports anonymous functions. See examples.
- append
lgl, if TRUE the text will be added as a new line after the line(s) specified in the match argument. If FALSE, then the text will replace the lines specified in the match argument
Value
(invisibly) FALSE if no lines in the specified file match the match argument and TRUE otherwise
Examples
tmpfile <- tempfile()
writeLines(text =
c("hello I am joe",
"this is multiple lines of text",
"12345",
"",
"^ line 4 is an empty line"),
con = tmpfile)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> this is multiple lines of text
#> 12345
#>
#> ^ line 4 is an empty line
# The simplest use is to append a line in a file with new text. Note that txt
# must be a single character string.
file_edit(file = tmpfile,
txt = "this line is appended after the second line",
match = 2,
append = TRUE)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> this is multiple lines of text
#> this line is appended after the second line
#> 12345
#>
#> ^ line 4 is an empty line
# We can instead replace a line using append = FALSE. Here, we replace the empty
# line in the file. After adding the line above, the empty line now occupies
# index 5.
file_edit(file = tmpfile,
txt = "this line is no longer empty",
match = 5,
append = FALSE)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> this is multiple lines of text
#> this line is appended after the second line
#> 12345
#> this line is no longer empty
#> ^ line 4 is an empty line
# The txt argument can also be a function, anonymous or named. It just needs to
# accept a single string and return a single string. Here, we replace "is" with
# "was" in line 6.
file_edit(file = tmpfile,
txt = ~ stringr::str_replace(.x, "is", "was"),
match = 6,
append = FALSE)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> this is multiple lines of text
#> this line is appended after the second line
#> 12345
#> this line is no longer empty
#> ^ line 4 was an empty line
# The match argument can also be a function. It just needs to accept a single
# string and return a single boolean. You can use it with the txt argument
# for some interesting interactions. Here, we change every line containing
# the word "is" to uppercase
file_edit(file = tmpfile,
txt = toupper,
match = ~ stringr::str_detect(.x, " is "),
append = FALSE)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> THIS IS MULTIPLE LINES OF TEXT
#> THIS LINE IS APPENDED AFTER THE SECOND LINE
#> 12345
#> THIS LINE IS NO LONGER EMPTY
#> ^ line 4 was an empty line
# strings containing carriage returns are preserved. Here, we use the readLines
# and length functions to ensure we append the string to the end of the file
multiline <-
"
Here is a string
that takes up multiple lines"
file_edit(file = tmpfile,
txt = multiline,
match = length(readLines(tmpfile)),
append = TRUE)
cat(readLines(tmpfile),sep = "\n")
#> hello I am joe
#> THIS IS MULTIPLE LINES OF TEXT
#> THIS LINE IS APPENDED AFTER THE SECOND LINE
#> 12345
#> THIS LINE IS NO LONGER EMPTY
#> ^ line 4 was an empty line
#>
#> Here is a string
#> that takes up multiple lines